feat: event bus integration and use cases

[evansenter]

Overview

PR #94 added the event bus infrastructure (SQLite-backed pub/sub with 6 tools). This issue tracks integrating it into clemini's workflow so it's actually useful.

Use Cases to Implement

1. Auto-registration on startup

• Register session automatically when clemini starts
• Use branch name or cwd as session name
• Unregister on clean exit

2. CI/build notifications

• Broadcast ci_completed, build_failed events
• Other sessions see results without polling GitHub

3. Discovery and coordination

• list_sessions to see who's working on what
• Avoid conflicting edits on same files
• Request help from other sessions (help_needed events)

4. Knowledge sharing

• gotcha_discovered - share non-obvious issues
• pattern_found - share useful patterns
• test_flaky - flag unreliable tests

5. Cross-repo coordination

• When creating issues in other repos, notify via repo:<name> channel
• Sessions working on that repo get notified

Implementation Tasks

• Add startup hook to auto-register session
• Add shutdown hook to unregister
• Periodic event polling (or integrate with main loop)
• System prompt guidance for when to broadcast/check events
• Consider desktop notifications for high-priority events

Dependencies

• Event bus tools from feat: add event bus for cross-session coordination (Phase 4) #94

Notes

The event bus is currently "plumbing without fixtures" - the infrastructure exists but nothing automatically uses it yet. This issue is about wiring it up.