[P0] Council Progress Visibility + Persistent Watch Until Terminal State

[simonholmes001]

Problem

Users see "no progress" and do not know whether to wait, retry, or exit. Watch currently idles out, which creates confusion.

Scope

• Keep watch alive until terminal status (completed or failed) unless user explicitly interrupts.
• Show explicit stages and elapsed time.
• Emit periodic backend heartbeat/progress events during long chunk prelude.
• Add adaptive polling backoff to reduce unnecessary load.

Acceptance Criteria

• Watch does not auto-stop on idle while run is active.
• Users see stage transitions and heartbeat timestamps.
• Poll frequency backs off over long runs and recovers on new progress.
• UX copy clearly explains what is happening and next expected state.