feat: Implement core Python FastAPI backend for user authentication, vault management, and file operations.

backend/auth/user_store.py

@@ -31,14 +31,22 @@ def _read() -> dict:
 
 def _write(data: dict):
     """Atomic write: write to .tmp then rename to prevent corruption."""
-    USERS_FILE.parent.mkdir(parents=True, exist_ok=True)
-    tmp = USERS_FILE.with_suffix(".tmp")
-    tmp.write_text(json.dumps(data, indent=2, default=str), encoding="utf-8")
-    shutil.move(str(tmp), str(USERS_FILE))
     try:
-        USERS_FILE.chmod(0o600)
-    except OSError:
-        pass  # Windows doesn't support Unix permissions
+        USERS_FILE.parent.mkdir(parents=True, exist_ok=True)
+        tmp = USERS_FILE.with_suffix(".tmp")
+        tmp.write_text(json.dumps(data, indent=2, default=str), encoding="utf-8")
+        shutil.move(str(tmp), str(USERS_FILE))
+        try:
+            USERS_FILE.chmod(0o600)
+        except OSError:
+            pass  # Windows doesn't support Unix permissions
+    except PermissionError as e:
+        logger.critical("=" * 60)
+        logger.critical(f"ERREUR DE PERMISSION : Impossible d'écrire dans {USERS_FILE.parent}")
+        logger.critical("Le conteneur n'a pas les droits sur le volume monté dans /app/data.")
+        logger.critical("FIX : Exécutez sur l'hôte (Linux) : sudo chown -R 1000:1000 /votre/chemin/data")
+        logger.critical("=" * 60)
+        raise e
 
 
 def has_users() -> bool: