Decide the kb command surface for the serverless default

[aksOps]

Question

What does bare kb do once the TUI exists - launch the TUI? Where do serve/web live during the transition and after deletion (kb serve keeps serving the frozen web until the deletion ticket, then API-only)? Which verbs appear in help, and does anything deprecate? A conversation, recorded as the resolution; it binds the deletion ticket.

Part of #80.

[aksOps]

Resolved (grilling, live): Target: bare kb launches the TUI; a non-TTY invocation prints help instead. kb serve becomes the explicit API-server verb. All existing CLI verbs unchanged. The flip happens ONCE, at the deletion ticket — until then bare kb keeps serving the frozen web UI and kb tui is explicit. One breaking change, made once, released as part of the map's final release.