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/KeyboardShortcutSettings.swift

@@ -45,35 +45,35 @@ enum KeyboardShortcutSettings {
 
         var label: String {
             switch self {
-            case .toggleSidebar: return "Toggle Sidebar"
-            case .newTab: return "New Workspace"
-            case .newWindow: return "New Window"
-            case .closeWindow: return "Close Window"
-            case .openFolder: return "Open Folder"
-            case .showNotifications: return "Show Notifications"
-            case .jumpToUnread: return "Jump to Latest Unread"
-            case .triggerFlash: return "Flash Focused Panel"
-            case .nextSurface: return "Next Surface"
-            case .prevSurface: return "Previous Surface"
-            case .nextSidebarTab: return "Next Workspace"
-            case .prevSidebarTab: return "Previous Workspace"
-            case .renameTab: return "Rename Tab"
-            case .renameWorkspace: return "Rename Workspace"
-            case .closeWorkspace: return "Close Workspace"
-            case .newSurface: return "New Surface"
-            case .toggleTerminalCopyMode: return "Toggle Terminal Copy Mode"
-            case .focusLeft: return "Focus Pane Left"
-            case .focusRight: return "Focus Pane Right"
-            case .focusUp: return "Focus Pane Up"
-            case .focusDown: return "Focus Pane Down"
-            case .splitRight: return "Split Right"
-            case .splitDown: return "Split Down"
-            case .toggleSplitZoom: return "Toggle Pane Zoom"
-            case .splitBrowserRight: return "Split Browser Right"
-            case .splitBrowserDown: return "Split Browser Down"
-            case .openBrowser: return "Open Browser"
-            case .toggleBrowserDeveloperTools: return "Toggle Browser Developer Tools"
-            case .showBrowserJavaScriptConsole: return "Show Browser JavaScript Console"
+            case .toggleSidebar: return String(localized: "shortcut.toggleSidebar.label", defaultValue: "Toggle Sidebar")
+            case .newTab: return String(localized: "shortcut.newWorkspace.label", defaultValue: "New Workspace")
+            case .newWindow: return String(localized: "shortcut.newWindow.label", defaultValue: "New Window")
+            case .closeWindow: return String(localized: "shortcut.closeWindow.label", defaultValue: "Close Window")
+            case .openFolder: return String(localized: "shortcut.openFolder.label", defaultValue: "Open Folder")
+            case .showNotifications: return String(localized: "shortcut.showNotifications.label", defaultValue: "Show Notifications")
+            case .jumpToUnread: return String(localized: "shortcut.jumpToUnread.label", defaultValue: "Jump to Latest Unread")
+            case .triggerFlash: return String(localized: "shortcut.flashFocusedPanel.label", defaultValue: "Flash Focused Panel")
+            case .nextSurface: return String(localized: "shortcut.nextSurface.label", defaultValue: "Next Surface")
+            case .prevSurface: return String(localized: "shortcut.previousSurface.label", defaultValue: "Previous Surface")
+            case .nextSidebarTab: return String(localized: "shortcut.nextWorkspace.label", defaultValue: "Next Workspace")
+            case .prevSidebarTab: return String(localized: "shortcut.previousWorkspace.label", defaultValue: "Previous Workspace")
+            case .renameTab: return String(localized: "shortcut.renameTab.label", defaultValue: "Rename Tab")
+            case .renameWorkspace: return String(localized: "shortcut.renameWorkspace.label", defaultValue: "Rename Workspace")
+            case .closeWorkspace: return String(localized: "shortcut.closeWorkspace.label", defaultValue: "Close Workspace")
+            case .newSurface: return String(localized: "shortcut.newSurface.label", defaultValue: "New Surface")
+            case .toggleTerminalCopyMode: return String(localized: "shortcut.toggleTerminalCopyMode.label", defaultValue: "Toggle Terminal Copy Mode")
+            case .focusLeft: return String(localized: "shortcut.focusPaneLeft.label", defaultValue: "Focus Pane Left")
+            case .focusRight: return String(localized: "shortcut.focusPaneRight.label", defaultValue: "Focus Pane Right")
+            case .focusUp: return String(localized: "shortcut.focusPaneUp.label", defaultValue: "Focus Pane Up")
+            case .focusDown: return String(localized: "shortcut.focusPaneDown.label", defaultValue: "Focus Pane Down")
+            case .splitRight: return String(localized: "shortcut.splitRight.label", defaultValue: "Split Right")
+            case .splitDown: return String(localized: "shortcut.splitDown.label", defaultValue: "Split Down")
+            case .toggleSplitZoom: return String(localized: "shortcut.togglePaneZoom.label", defaultValue: "Toggle Pane Zoom")
+            case .splitBrowserRight: return String(localized: "shortcut.splitBrowserRight.label", defaultValue: "Split Browser Right")
+            case .splitBrowserDown: return String(localized: "shortcut.splitBrowserDown.label", defaultValue: "Split Browser Down")
+            case .openBrowser: return String(localized: "shortcut.openBrowser.label", defaultValue: "Open Browser")
+            case .toggleBrowserDeveloperTools: return String(localized: "shortcut.toggleBrowserDevTools.label", defaultValue: "Toggle Browser Developer Tools")
+            case .showBrowserJavaScriptConsole: return String(localized: "shortcut.showBrowserJSConsole.label", defaultValue: "Show Browser JavaScript Console")
             }
         }
 
@@ -474,7 +474,7 @@ private class ShortcutRecorderNSButton: NSButton {
 
     func updateTitle() {
         if isRecording {
-            title = "Press shortcut…"
+            title = String(localized: "shortcut.pressShortcut.prompt", defaultValue: "Press shortcut…")
         } else {
             title = shortcut.displayString
         }