Add 'status' command to show current work

Show what Ava is currently working on.

Trigger

User sends: 'status' or 'what are you working on'

Response

If idle: 'I'm not working on anything right now. Send me a task ID to start.'

If working: 'Working on t-123: Add --help flag Phase: Reviewing (iteration 2/3) Started: 5 minutes ago'

Implementation

• Track current work state in TVar or similar
• Query subprocess status
• Format status message

Depends on

t-280.2.1 (need orchestrator subprocess infrastructure first)