Deploy worker to Fly.io with scale-to-zero

[abrichr]

Deploy the wright worker to Fly.io with scale-to-zero configuration.

Acceptance criteria:

• Dockerfile for worker
• fly.toml with scale-to-zero config
• Health check endpoint
• Secrets management for Supabase URL/key, GitHub token, Anthropic API key
• Deployment pipeline (manual or CI)

[abrichr]

Implemented in PR #15 (merged to main as e7287b1).