Fix architecture issues from todolist

- Add documentation warnings for in-memory rate limiting and failed login attempts
- Consolidate duplicate health endpoints into api/health.py
- Fix CLI to use correct async rescan method names
- Update download.py and anime.py to use custom exception classes
- Add WebSocket room validation and rate limiting

src/server/exceptions/__init__.py

@@ -144,6 +144,23 @@ class ConflictError(AniWorldAPIException):
         )
 
 
+class BadRequestError(AniWorldAPIException):
+    """Exception raised for bad request (400) errors."""
+
+    def __init__(
+        self,
+        message: str = "Bad request",
+        details: Optional[Dict[str, Any]] = None,
+    ):
+        """Initialize bad request error."""
+        super().__init__(
+            message=message,
+            status_code=400,
+            error_code="BAD_REQUEST",
+            details=details,
+        )
+
+
 class RateLimitError(AniWorldAPIException):
     """Exception raised when rate limit is exceeded."""