[MCP APP] Tools refresh fails — StatGPT Dev connector becomes unavailable in Claude; ChatGPT shows refresh_actions error but keeps working

### StatGPT Backend version

0.1.0

### Short description

Connector doesn't work after tool refresh

### What steps will reproduce the bug?

Claude/ChatGPT:

Go to Settings → Connectors
Connect / open StatGPT Dev connector
Trigger tools refresh (open connector / reconnect)
Observe connector state and browser console (Network/Console tab open)

### What is the expected behavior?

Tools refresh completes successfully
Tools appear in the connector
No refresh errors in the console
Connector is available and functional in both Claude and ChatGPT

### What do you see instead?

**Claude**:

Connector shows: "This connector's server is currently unavailable. Try again in a moment."
Tools do NOT appear
Console errors:
POST .../v1/toolbox/shttp/mcp/... 400 (Bad Request)
POST .../v1/toolbox/shttp/mcp/... 502 (Bad Gateway)
MCP app does not work

**ChatGPT**:

Console errors:
POST .../connectors/mcp/refresh_actions 424 (Failed Dependency) (repeats)
BUT the app still works — data grid renders and requests are processed despite the refresh error

### Additional information

_No response_