feat: Phase 1 complete — config persistante, single instance, restart, tray, logging, crash detection

1. Config persistante: AppConfig (vault_path, window x/y/w/h) sauvegardé dans %APPDATA%\ObsiGate\config.json
2. Single instance: tauri-plugin-single-instance — 2e lancement focus la fenêtre existante
3. Redémarrage backend: commande restart_backend + check_backend_health + restart auto après crash
4. Tray menu: Ouvrir, À propos, Quitter + clic gauche toggle fenêtre
5. Logging: env_logger + chrono → stdout/stderr du backend capturés dans logs/backend.log
6. Crash detection: boucle de monitoring toutes les 5s, notifie l'UI si le processus meurt

Dépendances ajoutées: tauri-plugin-store, tauri-plugin-single-instance, log, env_logger, chrono

desktop/Cargo.toml

@@ -15,10 +15,15 @@ tauri-plugin-dialog = "2"
 tauri-plugin-notification = "2"
 tauri-plugin-fs = "2"
 tauri-plugin-process = "2"
+tauri-plugin-store = "2"
+tauri-plugin-single-instance = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 reqwest = { version = "0.12", features = ["json"] }
 tokio = { version = "1", features = ["full"] }
+log = "0.4"
+env_logger = "0.11"
+chrono = "0.4"
 
 [features]
 default = ["custom-protocol"]