feat(terminal): wire CDC session-state streaming to /mux WebSocket (live sessionPatch delivery)

[Pritom14]

Problem

The /mux WebSocket delivers terminal PTY data and a session-state channel (ch: sessions) to the frontend MuxProvider. The PTY path works. The session-state path did not: the server was sending thin CDC notification objects (seq, sessionId, eventType) that do not match the SessionPatch shape (id, status, activity, attentionLevel, lastActivityAt) the TypeScript consumer expects. As a result, the dashboard never received live session-state updates over the WebSocket -- it had to poll or wait for a page refresh.

Root cause

terminal.Manager subscribed to the CDC broadcaster but forwarded raw cdc.Event fields directly onto the wire. There was no concept of a SessionSource interface to resolve derived session state (PR facts + canonical lifecycle -> display status), and no attentionLevel mapping on the server side.

What this issue tracks

Wire the full CDC -> derived-state -> SessionPatch delivery path through /mux:

• Define a SessionSource interface in the terminal package (clean boundary: terminal does not import the service layer)
• Implement DeriveStatus in the domain package (it only uses domain types; pulling it out of the service layer removes the circular pressure)
• Implement attentionLevel() server-side, mirroring getDetailedAttentionLevel in packages/web/src/lib/types.ts
• Build daemonSessionSource in the daemon package: wraps the sqlite store + GetDisplayPRFactsForSession + DeriveStatus
• Move DB enrichment off the CDC broadcaster hot path (the broadcaster contract explicitly requires non-blocking callbacks)
• Close the subscribe/snapshot gap so no event is missed during initial connect
• Add full unit coverage for the attention-level mapping and functional integration tests for the end-to-end wire path