Implements GitHub API provider following the same pattern as Gitea:
- Full PR operations (create, get, list, merge, update, close)
- Branch operations via API
- Comment and label management
- Reviewer request support
- Rate limit error handling
Server enhancements:
- Auto-detect provider from repository URL (github.com vs custom Gitea)
- Initialize GitHub provider when token is configured
- Health check includes both provider statuses
- Token selection based on repo URL for clone/push operations
Refs: #110🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>