feat: french translation (#802)

* Add French (fr) language support

- Create app/src/i18n/locales/fr/translation.json with full UI translations
- Register French in SUPPORTED_LANGUAGES and i18next resources
- Wire French locale from date-fns for relative date formatting

* Fix Vite file watcher EBUSY error on Windows by excluding Rust target directory

tauri/vite.config.ts

@@ -27,7 +27,7 @@ export default defineConfig({
     strictPort: true,
     // Watch files in the app directory for changes
     watch: {
-      ignored: ['!**/../app/**'],
+      ignored: ['!**/../app/**', '**/target/**'],
     },
   },
   envPrefix: ['VITE_', 'TAURI_'],