Add backlinks in GitHub comments and PR descriptions

## Task Add backlinks in GitHub comments and PR descriptions to link back to application resources. ## Requirements 1. **Application URL configuration** - Add environment variable (e.g., `APP_URL`) to set the base URL of the application 2. **GitHub integration updates** - When agents post to GitHub, include backlinks to: - Ticket detail pages - Proposals - Agent sessions/logs - Any other relevant resources 3. **Places to add links**: - PR descriptions created by workers - PR comments when updating/reviewing - Issue comments (if applicable) ## Implementation 1. Add `APP_URL` to environment configuration 2. Create helper methods to generate URLs for resources 3. Update git-workflow skill and any code that posts to GitHub 4. Format links clearly so users can navigate back and forth ## Example A PR description might include: ``` Implements ticket #42: Add feature X View ticket: https://app.example.com/tickets/42 View agent session: https://app.example.com/agent-sessions/123 ``` ## Notes - Handle case where APP_URL is not set (don't add links or use placeholder) - Ensure links are properly formatted for GitHub markdown