feat: add job detail and listing pages with real-time status (#27)

- Replace placeholder job detail page with functional implementation
  that fetches from job_queue and job_events tables via Supabase
- Show status badge, repo URL, task, cost, branch, timestamps, and
  error details
- Display job events as a visual timeline with icons per event type
- Auto-refresh every 5 seconds while job is in progress (queued/
  claimed/running)
- Add jobs listing page at /jobs with recent jobs table (limit 20)
- Add "Jobs" link to landing page and detail page nav bars
- Error state when job not found

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: abrichr