fix: resolve issue-facade ID mapping bugs and enhance functionality

- Fix Sentinel bug in list command where Click set search params to Sentinel.UNSET
- Fix version command by adding explicit version and package_name parameters
- Fix test isolation by correcting mock patch targets and datetime objects
- Fix critical ID mapping bug: use issue.number consistently instead of mixing with issue.backend_id
- Update all comment operations to use issue numbers instead of internal IDs
- Ensure issue-facade uses upstream issue numbers directly without local ID confusion
- Add comprehensive test coverage with 20 passing tests
- Verify core functionality: list, show, close, version, backend management all working
- Successfully close issue #166 with proper comment handling

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

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

issue_tracker/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
+"""