bug: Nonexistent User Endpoint

The MCP server's `get_user` tool attempts to call:
```
GET /api/v1/users/me/
```

**Problem:** This endpoint:
- Returns 404 in Plane v0.28.0
- The documentation at https://developers.plane.so/api-reference shows no "user" endpoints at all, just workspace and project members.
- A user endpoint DOES exist at `/api/users/me/` but it seems to require session authentication, not API key authentication

