[bug] TUI subscribes to brain/{sessionID} but server publishes to brain/status before any session exists

[four-bytes-robby]

Bug

The brain TUI sidebar (src/tui.tsx) subscribes to brain/{sessionId} when a session ID is available, and brain/status otherwise. The server (src/status.ts) starts publishing on the default brain/status channel and only switches to brain/{sessionID} after a session is created (via chat.message hook).

Repro

1. Open a project where brain has not yet indexed all files
2. Watch the TUI sidebar during initial ingest — no status updates appear (bus subscription is on the wrong channel)
3. HTTP fallback eventually shows the state, but real-time push is broken

Fix

TUI must always subscribe to brain/status (catches pre-session ingest), and additionally subscribe to brain/{sessionID} once a session ID is available (catches post-chat events after server switches).