Add project documentation and license

- README.md: usage, requirements, features, and configuration
- AGENTS.md: guidelines for AI agents working on the codebase
- LICENSE: MIT license

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

AGENTS.md

@@ -0,0 +1,64 @@
+# AGENTS.md
+
+Guidelines for AI agents working on this codebase.
+
+## Project Overview
+
+This is a Python CLI tool for Debian package maintainers. It tracks packages with new upstream versions by querying the Debian UDD database.
+
+## Architecture
+
+- Single-file CLI application using Click for command handling
+- Rich library for terminal output (tables and formatting)
+- python-debian library for parsing APT Sources files
+- JSON-based caching for performance
+
+## Key Components
+
+### Data Flow
+1. `fetch_todo_list()` - Downloads JSON from UDD
+2. `filter_todo_list()` - Removes non-upstream items and pre-releases
+3. `load_source_info_map()` - Parses APT Sources for Vcs-Git and uploaders
+4. `list_todos()` - Renders output table
+
+### Important Patterns
+- Version normalization strips epoch and Debian revision
+- Pre-release detection via regex (`alpha`, `beta`, `rc`, `a`, `b`)
+- Team extraction from Vcs-Git URLs on salsa.debian.org
+- Cache invalidation based on Sources file mtimes
+
+## Code Style
+
+- Type hints throughout (Python 3.10+ syntax)
+- No external config files; constants at module top
+- Functions are pure where possible
+- Error handling is minimal; tool is for personal use
+
+## Testing
+
+No test suite. Manual testing with:
+```bash
+./todo list
+./todo list --show-prerelease
+./todo update
+```
+
+## Common Tasks
+
+### Adding a new filter
+Modify `filter_todo_list()` to add conditions.
+
+### Changing output columns
+Edit `list_todos()` - both table and narrow-mode branches.
+
+### Updating cache format
+Increment `CACHE_VERSION` to invalidate old caches.
+
+## Dependencies
+
+System packages (Debian):
+- python3-click
+- python3-debian
+- python3-rich
+
+No pip/venv setup; uses system Python.