feat: implement universal issue tracking facade

Add comprehensive issue tracking facade system that provides a unified CLI interface to any issue tracking backend. The facade automatically detects the repository's issue tracker and provides consistent commands across all platforms.

Key features:
- Repository-aware automatic backend detection (GitHub, GitLab, Gitea, local SQLite)
- Unified CLI interface with same commands across all backends
- Plugin architecture for extensible backend support
- Local SQLite backend for offline development
- Gitea backend with full API integration
- Bidirectional synchronization between backends
- Performance-optimized domain models with caching
- Clean architecture with separation of concerns

The facade acts as a "universal remote control" for issue tracking systems, eliminating the need to learn different CLIs for each platform while providing seamless offline capability and cross-platform consistency.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

issue-facade/backends/__init__.py

@@ -0,0 +1,11 @@
+"""
+Issue Tracking Backend Plugins
+
+This package contains implementations for various issue tracking backends.
+Each backend implements the IssueBackend interface to provide a consistent
+API regardless of the underlying issue tracking system.
+
+Available Backends:
+- local: SQLite-based local backend for offline use
+- gitea: Gitea API backend for GitHub-compatible systems
+"""