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/TerminalNotificationStore.swift

@@ -545,10 +545,10 @@ final class TerminalNotificationStore: ObservableObject {
         }
 
         let alert = notificationSettingsAlertFactory()
-        alert.messageText = "Enable Notifications for cmux"
-        alert.informativeText = "Notifications are disabled for cmux. Enable them in System Settings to see alerts."
-        alert.addButton(withTitle: "Open Settings")
-        alert.addButton(withTitle: "Not Now")
+        alert.messageText = String(localized: "dialog.enableNotifications.title", defaultValue: "Enable Notifications for cmux")
+        alert.informativeText = String(localized: "dialog.enableNotifications.message", defaultValue: "Notifications are disabled for cmux. Enable them in System Settings to see alerts.")
+        alert.addButton(withTitle: String(localized: "dialog.enableNotifications.openSettings", defaultValue: "Open Settings"))
+        alert.addButton(withTitle: String(localized: "dialog.enableNotifications.notNow", defaultValue: "Not Now"))
         alert.beginSheetModal(for: window) { [weak self] response in
             guard response == .alertFirstButtonReturn,
                   let url = URL(string: "x-apple.systempreferences:com.apple.preference.notifications") else {