Wire or gate MCP server lifecycle actions

[thinmintdev]

What to build

The MCP lifecycle route POST /api/mcp/{server_id}/{action} still returns 501 mcp.supervisor_unavailable for start/stop/restart, and health reports mcp_supervisor=false. Wire the supervisor path or hide/gate lifecycle actions so users do not hit placeholder behavior.

Acceptance criteria

• start/stop/restart either execute through a real supervisor or are not exposed as available actions.
• /api/health capability flags match the exposed behavior.
• Dashboard/API tests cover both available and unavailable lifecycle states.
• 501 placeholder behavior is removed from normal user-facing flows.

Blocked by

None - can start immediately