Add a language-switch system with per-language files

Introduce a hand-rolled i18n layer across all three UIs, each reading its
text from per-language JSON files (English base + Polish + Danish). Nothing
in the converted screens hardcodes English any more.

- Web App (Vue): src/i18n/{en,pl,da}.json + index.js exposing t()/tSplit(),
  reactive to the signed-in profile locale. Every view, component, form and
  the status labels in lib/format.js go through t().
- API Server panel (Vue): src/i18n/ with its own localStorage-persisted
  language (the panel has no user profile) and a header language picker.
  Chrome, cards, login and API section titles translated; endpoint reference
  descriptions intentionally kept in English. Rebuilt embedded dist.
- Phone App (Flutter): assets/i18n/ + lib/i18n.dart loaded at startup,
  driven by AppSettings.locale. Nav, login, lock, dashboard, the full
  Settings panel (incl. language picker) and format.dart status labels
  translated; remaining detail screens fall back to English.

Language = the language half of the existing BCP-47 locale; the region half
still drives date/number/currency formatting. Missing keys fall back to
English, and plurals use Intl.PluralRules / Intl.plural so Polish gets the
correct one/few/many forms. Settings flags languages without a translation.

Tests updated to assert the localized (Polish) status wording; all pass.
See TRANSLATIONS.md for the format and how to add a language.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Web App/web/src/api.js

@@ -1,6 +1,7 @@
 // Single client for the Car Control API Server. The web app never talks to
 // PocketBase directly — only to these endpoints (proxied to the API Server in
 // dev via vite.config.js).
+import { t } from "./i18n";
 
 // Default API base: the Vite env override, else the same-origin "/api" (proxied
 // to the API Server in dev). A user can override this at runtime via the login
@@ -39,7 +40,7 @@ async function handleResponse(res, path) {
     localStorage.removeItem(TOKEN_KEY);
     localStorage.removeItem(USER_KEY);
     if (location.pathname !== "/login") location.href = "/login";
-    throw new Error("Session expired — please log in again.");
+    throw new Error(t("errors.sessionExpired"));
   }
 
   if (res.status === 204) return null;