Fix: connect to memsprout from Claude at mcp.memsprout.com/mcp

Connecting Claude (Desktop or claude.ai) to the custom domain failed with "Authorization with the MCP server failed." Tracing the live OAuth flow showed Claude completing the whole handshake — discovery, registration, login, and token issuance all succeeded — and then silently giving up before making a single authenticated call. The trigger was the bare-domain server URL: Claude's connector aborts after token exchange when the OAuth resource is an origin root, but works when it has a path (which is why the raw edge-function URL always connected). The MCP server now lives at a path, https://mcp.memsprout.com/mcp, so it behaves like any conventional MCP endpoint. Reconnect using the /mcp URL. The bare-domain and legacy vello-mcp.matteo-3bc.workers.dev URLs keep working for already-connected clients.