Upgrade i18next to v26, fix breaking changes

- i18next 25.10.4 → 26.0.1, react-i18next 16.6.1 → 17.0.1
- Replace removed `initImmediate: false` with `initAsync: false`
- Remove `showSupportNotice` option (removed in v26)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/i18n/src/index.ts

@@ -23,8 +23,7 @@ export function initI18n() {
       interpolation: {
         escapeValue: false,
       },
-      showSupportNotice: false,
-      initImmediate: false,
+      initAsync: false,
     });
 }