- tui_gateway: new `setup.status` RPC that reuses CLI's
`_has_any_provider_configured()`, so the TUI can ask the same question
the CLI bootstrap asks before launching a session
- useSessionLifecycle: preflight `setup.status` before both `newSession`
and `resumeById`, and render a clear "Setup Required" panel when no
provider is configured instead of booting a session that immediately
fails with `agent init failed`
- createGatewayEventHandler: drop duplicate startup resume logic in
favor of the preflighted `resumeById`, and special-case the
no-provider agent-init error as a last-mile fallback to the same
setup panel
- add regression tests for both paths
