Uninstall kcap from the macOS app menu #1786

Dragging kcap.app to the Trash runs nothing, and macOS gives an app no uninstall hook. What it leaves behind:

• the daemon's LaunchAgent, still pointing at the deleted bundle
• the local server, still running
• the kcap link on PATH, now dangling, so every harness hook fails with "command not found"
• the harness hooks, skills, MCP entries and ~/.config/kcap

Add an Uninstall kcap… app-menu item on macOS. It removes all of that, then moves the app to the Trash. When a local server is installed, the confirmation warns that its recorded sessions are permanently deleted.

The menu item runs kcap uninstall, which needs fixing on every platform:

• It never removes the local server. Its default root is ~/.config/kcap/local, so the final config delete wipes the server's data while its LaunchAgent keeps running.
• It ends hosted agents without checking whether any are running.
• It leaves the kcap link on PATH.

Linux is #1782. Windows already cleans up through its Velopack uninstall hook.