NewYearsCards v0.2.0

Added

• Comprehensive unit tests covering address processing, Sheets URL parsing, and CLI.
• --dry-run for build-labels to preview output without writing files.
• Console script wiring in pyproject.toml (entry newyearscards).
• Core modules: sheets.py, addresses.py, and config.py.

Changed

• Moved non-essential documentation into docs/ and updated references in README.
• README and workflow documentation aligned with actual CLI behavior.
• Lazy-load Google auth in downloader to avoid unnecessary runtime deps for non-download commands.