MCP catalog presets, acts-as identity and personal connections

In the UI: the MCP servers page becomes a catalog of presets showing which active agents use each one and what archiving would affect. The agent detail page gains an MCP tab listing the agent’s effective servers, their identity and connection state, with flows to add a preset or custom HTTP server and to revoke a connection. People can see and revoke the MCP sign-ins they granted.

In agent config: an MCP entry can reference a preset with catalog:<name> and say whose sign-in its calls use with actsAs (none, service, user or user_or_service):

{ "github": { "use": "catalog:github", "actsAs": "user" } }

See MCP and MCP credentials. #3726, #3675, #3638