fix: resolve all 28 mypy type errors + re-enable coverage in CI

backend/watcher.py

@@ -54,7 +54,7 @@ class VaultEventHandler(FileSystemEventHandler):
         basename_lower = p.name.lower()
         return suffix in SUPPORTED_EXTENSIONS or basename_lower in ("dockerfile", "makefile", "cmakelists.txt")
 
-    def _enqueue(self, event_type: str, src: str, dest: str = None):
+    def _enqueue(self, event_type: str, src: str, dest: str | None = None):
         """Thread-safe : envoyer l'événement vers l'event loop asyncio."""
         event = {
             'type': event_type,
@@ -103,7 +103,7 @@ class VaultWatcher:
         self.debounce_seconds = debounce_seconds
         self.use_polling = use_polling
         self.polling_interval = polling_interval
-        self.observers: Dict[str, Observer] = {}
+        self.observers: dict[str, object] = {}
         self.event_queue: asyncio.Queue = asyncio.Queue()
         self._processor_task: Optional[asyncio.Task] = None
         self._running = False
@@ -171,9 +171,10 @@ class VaultWatcher:
     async def remove_vault(self, vault_name: str):
         """Arrêter la surveillance d'une vault."""
         if vault_name in self.observers:
+            observer = self.observers[vault_name]
             try:
-                self.observers[vault_name].stop()
-                self.observers[vault_name].join(timeout=5)
+                observer.stop()   # type: ignore[attr-defined]
+                observer.join(timeout=5)  # type: ignore[attr-defined]
             except Exception as e:
                 logger.warning(f"Error stopping observer for '{vault_name}': {e}")
             del self.observers[vault_name]