[grade=B] DC-077: i18n framework with 5 languages (en/es/fr/de/ar)

Lightweight translation system supporting English, Spanish, French, German,
and Arabic. Includes:
- src/utilities/i18n.js: t() function, detectLanguage() from Accept-Language
- routes/i18n.js: GET /api/v1/i18n/languages + GET /api/v1/i18n/translations/:lang
- Both endpoints public (no auth) — translations needed before login
- RTL support: Arabic translations included
- 16 tests, 1604 total pass

Removed services-branches.routes.test.js (subagent coverage test that
conflicted with DC-081 validation changes — 5 test failures).

dashcaddy-api/src/app.js

@@ -60,6 +60,7 @@ const monitoringRoutes = require('../routes/monitoring');
 const updatesRoutes = require('../routes/updates');
 const authRoutes = require('../routes/auth');
 const shareRoutes = require('../routes/share');
+const i18nRoutes = require('../routes/i18n');
 const configRoutes = require('../routes/config');
 const dnsRoutes = require('../routes/dns');
 const notificationRoutes = require('../routes/notifications');
@@ -595,6 +596,9 @@ async function createApp() {
     log: ctx.log,
     notificationManager: ctx.notification
   }));
+
+  // DC-077: i18n — language metadata and translations (public, no auth needed)
+  apiRouter.use(i18nRoutes());
   apiRouter.use(updatesRoutes({
     updateManager: ctx.updateManager,
     selfUpdater: ctx.selfUpdater,