Internationalization: 7 languages with live switching

Custom signal-based runtime (no i18n dependency): shared src/shared/i18n
dictionaries, ui I18nService.t() reactive by construction so language
switches live, and a backend i18n.ts for native menus + thrown errors.
Every user-facing string keyed across templates, toasts, dialogs, file
kinds, columns, macOS menu/context menus, and errors. Language picker in
Options (auto-detects OS locale, falls back to English); switching
relabels the webview and native chrome instantly. English/Spanish/French/
German fully drafted; Chinese/Japanese/Basque drafted, flagged for native
review. Docs updated.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/architecture.md

@@ -154,7 +154,14 @@ would float over editor windows).
   remembered (`FileActionsService.menuTarget`). Labels are per-platform.
 - `menu.ts` — macOS-only app menu, rebuilt on every connections change (the
   Connect submenu mirrors the store). ⌘W is intercepted by the menu, so bun
-  routes `close-tab` to the focused editor window first.
+  routes `close-tab` to the focused editor window first. Labels go through
+  backend `i18n.t` and the menu is rebuilt on a locale change too.
+- `i18n.ts` — backend translator (native menus + thrown error messages, which
+  no Angular service can reach). `setLocale(setting)` caches the resolved
+  locale (from `settings.locale`, `system` via `Intl…resolvedOptions().locale`);
+  `t(key, params)` shares the same `src/shared/i18n` dictionaries as the UI.
+  Wired in index.ts on boot and on `settingsChanged` (relocalizes + rebuilds
+  the app menu). `context-menu.ts` labels resolve through `t()` at show-time.
 - `tray.ts` — static icon, click = activate main. macOS template image;
   Windows colored icon. No `setImage` calls ever (they lose the template
   treatment) and no menu (clicks arrive directly).
@@ -202,6 +209,15 @@ would float over editor windows).
   (whose constructor spawns a workspace — fatal in secondary windows).
 - `connections.service.ts` — store mirror + ssh-config hosts; reloads on the
   `connectionsChanged` push.
+- `i18n.service.ts` — runtime translator. `locale` signal + `t('ns.key', params)`
+  (dotted lookup, `{param}` interpolation, `{one,other}` plural maps via
+  `Intl.PluralRules`); missing keys fall back to English then the raw key.
+  **Reactive by design**: `t()` reads the `locale` signal, so every template
+  binding that calls it re-renders live on a language switch (same call-stack
+  tracking as `iconClass`) — no pipe. Also exposes locale-aware `date()`/`size()`
+  /`speed()` so the file list reformats on switch. `SettingsService.applyLocale`
+  resolves the `locale` setting (`system` → `navigator.language`) into it, on
+  boot and on the `settingsChanged` broadcast (so editor/manager windows follow).
 - `file-actions.service.ts` — toolbar/keyboard/context-menu file ops, always
   against an explicit panel; `menuTarget` remembers the right-clicked row.
 - `file-icons.ts` — extension → category map driving glyphs, colors