feat: add Japanese localization with String Catalog (#819)

* Add i18n infrastructure with String Catalog and Japanese translations

Introduce String Catalog (.xcstrings) for localization support:
- Localizable.xcstrings: 195 UI string entries with en and ja translations
- InfoPlist.xcstrings: Info.plist strings (microphone usage, Finder menu items)
- project.pbxproj: add xcstrings to build phase and ja to knownRegions

* Replace hardcoded UI strings with String(localized:defaultValue:)

Migrate all user-facing strings across 11 source files to use
String(localized:defaultValue:) API (macOS 13+). Each string references
a key in Localizable.xcstrings, with the English text preserved as
defaultValue for fallback.

Files modified:
- KeyboardShortcutSettings: 28 shortcut labels
- SocketControlSettings: mode names and descriptions
- TabManager: placement labels, color names, close dialogs
- BrowserPanel/BrowserPanelView: error pages, context menus, tooltips
- UpdateViewModel/UpdatePopoverView/UpdatePill: update UI states
- NotificationsPage: notification panel labels
- SurfaceSearchOverlay: search bar placeholder and tooltips
- AppDelegate: menus, dialogs, command palette items

* Fix localization gaps from review feedback

Address review comments from CodeRabbit, Greptile, and Cubic Dev AI:
- Use interpolated String(localized:) instead of concatenation for
  version/progress strings in UpdateViewModel
- Localize remaining hardcoded strings in AppDelegate: window labels,
  rename dialog, status menu items, unread notification count
- Localize insecure HTTP alert body in BrowserPanel
- Add 12 new entries to Localizable.xcstrings with Japanese translations

* Fix String(localized:defaultValue:) keys to use StaticString

The localized: parameter requires StaticString when defaultValue: is
used. Move string interpolation from the key to defaultValue only,
and revert maxWidthText to plain strings since they are only used for
layout width calculation.

* Localize remaining UI strings across all source files

Add String(localized:defaultValue:) to all user-facing strings in:
- cmuxApp.swift: settings screen, menus, about panel, dialogs (~180 strings)
- ContentView.swift: command palette, sidebar context menu, dialogs (~200 strings)
- Workspace.swift: rename/move/close tab dialogs, tooltips (~20 strings)
- UpdateTitlebarAccessory.swift: titlebar tooltips, notifications popover (~10 strings)
- TerminalNotificationStore.swift: notification permission dialog (4 strings)
- CmuxWebView.swift: browser context menu items (2 strings)
- AppDelegate.swift: CLI install/uninstall alerts (6 strings)

Add 418 new entries to Localizable.xcstrings with Japanese translations.
Extract sidebar context menu into separate @ViewBuilder to fix Swift
type-checker timeout in large body.
Fix xcstrings format specifiers for interpolated strings (%lld, %@).

Total: 624 localization entries covering the full UI.

* Address review feedback: fix missing localizations and terminology

- Localize javaScriptDialogTitle URL branch in BrowserPanel
- Localize cantReach error message in BrowserPanel
- Localize close other tabs dialog message in TabManager
- Localize workspace accessibility label in ContentView
- Fix unread notification singular/plural (split into two keys)
- Fix insecure connection apostrophe inconsistency (unify to U+2019)
- Rename socketControl.fullOpen.description to socketControl.allowAll.description
- Remove dead code: renameTargetNoun function
- Fix terminology inconsistencies in xcstrings:
  - Unify "Developer Tools" to デベロッパツール
  - Unify "Jump to Latest Unread" phrasing
  - Unify "Flash Focused Panel" terminology
  - Fix dialog.enableNotifications.notNow translation

* fix: address remaining PR 819 review feedback

* fix: use a single localized key for close-other-tabs

* fix: avoid inflection markup in close-other-tabs message

* Address review feedback: localize tooltip, fix subtitle concat, unify keys

- Localize menubar tooltip unread count (hardcoded English -> localized)
- Replace subtitle string concatenation anti-pattern with single localized
  keys containing interpolation placeholders
- Unify workspace fallback key to workspace.displayName.fallback
- Remove unused workspace.defaultName key from xcstrings
- Add Japanese translations for new tooltip and subtitle keys

Sources/Workspace.swift

@@ -990,10 +990,10 @@ final class Workspace: Identifiable, ObservableObject {
 
     private static func currentSplitButtonTooltips() -> BonsplitConfiguration.SplitButtonTooltips {
         BonsplitConfiguration.SplitButtonTooltips(
-            newTerminal: KeyboardShortcutSettings.Action.newSurface.tooltip("New Terminal"),
-            newBrowser: KeyboardShortcutSettings.Action.openBrowser.tooltip("New Browser"),
-            splitRight: KeyboardShortcutSettings.Action.splitRight.tooltip("Split Right"),
-            splitDown: KeyboardShortcutSettings.Action.splitDown.tooltip("Split Down")
+            newTerminal: KeyboardShortcutSettings.Action.newSurface.tooltip(String(localized: "workspace.tooltip.newTerminal", defaultValue: "New Terminal")),
+            newBrowser: KeyboardShortcutSettings.Action.openBrowser.tooltip(String(localized: "workspace.tooltip.newBrowser", defaultValue: "New Browser")),
+            splitRight: KeyboardShortcutSettings.Action.splitRight.tooltip(String(localized: "workspace.tooltip.splitRight", defaultValue: "Split Right")),
+            splitDown: KeyboardShortcutSettings.Action.splitDown.tooltip(String(localized: "workspace.tooltip.splitDown", defaultValue: "Split Down"))
         )
     }
 
@@ -3331,15 +3331,15 @@ final class Workspace: Identifiable, ObservableObject {
               let panel = panels[panelId] else { return }
 
         let alert = NSAlert()
-        alert.messageText = "Rename Tab"
-        alert.informativeText = "Enter a custom name for this tab."
+        alert.messageText = String(localized: "dialog.renameTab.title", defaultValue: "Rename Tab")
+        alert.informativeText = String(localized: "dialog.renameTab.message", defaultValue: "Enter a custom name for this tab.")
         let currentTitle = panelCustomTitles[panelId] ?? panelTitles[panelId] ?? panel.displayTitle
         let input = NSTextField(string: currentTitle)
-        input.placeholderString = "Tab name"
+        input.placeholderString = String(localized: "dialog.renameTab.placeholder", defaultValue: "Tab name")
         input.frame = NSRect(x: 0, y: 0, width: 240, height: 22)
         alert.accessoryView = input
-        alert.addButton(withTitle: "Rename")
-        alert.addButton(withTitle: "Cancel")
+        alert.addButton(withTitle: String(localized: "common.rename", defaultValue: "Rename"))
+        alert.addButton(withTitle: String(localized: "common.cancel", defaultValue: "Cancel"))
         let alertWindow = alert.window
         alertWindow.initialFirstResponder = input
         DispatchQueue.main.async {
@@ -3368,24 +3368,24 @@ final class Workspace: Identifiable, ObservableObject {
         )
 
         var options: [(title: String, destination: PanelMoveDestination)] = [
-            ("New Workspace in Current Window", .newWorkspaceInCurrentWindow),
-            ("Selected Workspace in New Window", .selectedWorkspaceInNewWindow),
+            (String(localized: "dialog.moveTab.newWorkspaceCurrentWindow", defaultValue: "New Workspace in Current Window"), .newWorkspaceInCurrentWindow),
+            (String(localized: "dialog.moveTab.selectedWorkspaceNewWindow", defaultValue: "Selected Workspace in New Window"), .selectedWorkspaceInNewWindow),
         ]
         options.append(contentsOf: workspaceTargets.map { target in
             (target.label, .existingWorkspace(target.workspaceId))
         })
 
         let alert = NSAlert()
-        alert.messageText = "Move Tab"
-        alert.informativeText = "Choose a destination for this tab."
+        alert.messageText = String(localized: "dialog.moveTab.title", defaultValue: "Move Tab")
+        alert.informativeText = String(localized: "dialog.moveTab.message", defaultValue: "Choose a destination for this tab.")
         let popup = NSPopUpButton(frame: NSRect(x: 0, y: 0, width: 320, height: 26), pullsDown: false)
         for option in options {
             popup.addItem(withTitle: option.title)
         }
         popup.selectItem(at: 0)
         alert.accessoryView = popup
-        alert.addButton(withTitle: "Move")
-        alert.addButton(withTitle: "Cancel")
+        alert.addButton(withTitle: String(localized: "dialog.moveTab.move", defaultValue: "Move"))
+        alert.addButton(withTitle: String(localized: "common.cancel", defaultValue: "Cancel"))
 
         guard alert.runModal() == .alertFirstButtonReturn else { return }
         let selectedIndex = max(0, min(popup.indexOfSelectedItem, options.count - 1))
@@ -3431,9 +3431,9 @@ final class Workspace: Identifiable, ObservableObject {
         if !moved {
             let failure = NSAlert()
             failure.alertStyle = .warning
-            failure.messageText = "Move Failed"
-            failure.informativeText = "cmux could not move this tab to the selected destination."
-            failure.addButton(withTitle: "OK")
+            failure.messageText = String(localized: "dialog.moveFailed.title", defaultValue: "Move Failed")
+            failure.informativeText = String(localized: "dialog.moveFailed.message", defaultValue: "cmux could not move this tab to the selected destination.")
+            failure.addButton(withTitle: String(localized: "common.ok", defaultValue: "OK"))
             _ = failure.runModal()
         }
     }
@@ -3500,11 +3500,11 @@ extension Workspace: BonsplitDelegate {
     @MainActor
     private func confirmClosePanel(for tabId: TabID) async -> Bool {
         let alert = NSAlert()
-        alert.messageText = "Close tab?"
-        alert.informativeText = "This will close the current tab."
+        alert.messageText = String(localized: "dialog.closeTab.title", defaultValue: "Close tab?")
+        alert.informativeText = String(localized: "dialog.closeTab.message", defaultValue: "This will close the current tab.")
         alert.alertStyle = .warning
-        alert.addButton(withTitle: "Close")
-        alert.addButton(withTitle: "Cancel")
+        alert.addButton(withTitle: String(localized: "dialog.closeTab.close", defaultValue: "Close"))
+        alert.addButton(withTitle: String(localized: "common.cancel", defaultValue: "Cancel"))
 
         // Prefer a sheet if we can find a window, otherwise fall back to modal.
         if let window = NSApp.keyWindow ?? NSApp.mainWindow {