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/local/__init__.py

@@ -0,0 +1,19 @@
+"""
+Local SQLite Backend
+
+A local, file-based issue tracking backend using SQLite for storage.
+This backend provides complete offline functionality and serves as the
+reference implementation for the backend interface.
+
+Features:
+- Full CRUD operations
+- SQLite database storage
+- No external dependencies
+- Offline operation
+- Fast local search
+- Backup and export capabilities
+"""
+
+from .backend import LocalSQLiteBackend
+
+__all__ = ['LocalSQLiteBackend']