Export EnsurePicoChannel and reuse it during launcher and gateway startup
so the Pico channel is initialized earlier with a generated token when
needed.
Also extend backend tests to cover startup-time Pico setup behavior and
keep the setup path idempotent.
Normalize missing security sections when attaching, loading, and saving
security config so existing config files without `.security.yml` can still
be updated safely. This fixes Pico channel setup for legacy/existing configs
and adds coverage for the missing security file path and unexported JSON
field behavior.
* feat(gateway): support hot reload and empty startup
- extract gateway runtime into pkg/gateway
- add gateway.hot_reload config with default and example values
- allow starting the gateway without a default model via --allow-empty
- stop treating missing enabled channels as a startup error
- update related tests
* feat: replace gateway SSE updates with polling-based state sync
- remove gateway SSE broadcasting and event endpoint
- add polling-based gateway status refresh with stopping state handling
- detect when gateway restart is required after default model changes
- resolve gateway health and websocket proxy targets from configured host
- update gateway UI labels and add backend/frontend test coverage
* fix: Use secure defaults for Pico channel setup and stop leaking the token in the URL
* fix: Derive default allow_origins from the setup request's Origin header instead of hardcoding localhost ports
wenjie