Why

reapplies #22386 which was previously reverted

Also, introduce remoteControl/enable and remoteControl/disable app-server APIs to toggle on/off remote control at runtime for a given running app-server instance.

What Changed

• Adds experimental v2 RPCs:
  • remoteControl/enable
  • remoteControl/disable
• Adds RemoteControlRequestProcessor and routes the new RPCs through it instead of ConfigRequestProcessor.
• Adds named RemoteControlHandle::enable, disable, and status methods.
• Makes remoteControl/enable return an error when sqlite state DB is unavailable, while keeping enrollment/websocket failures as async status updates.
• Adds AppServerRuntimeOptions.remote_control_enabled and hidden --remote-control flags for codex app-server and codex-app-server.
• Updates managed daemon startup to use codex app-server --remote-control --listen unix://.
• Marks Feature::RemoteControl as removed and ignores [features].remote_control.
• Updates app-server README entries for the new remote-control methods.