chore: prepare release v3.0.0

docs/releases/v3.0.0.md

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+# MTG Python Deckbuilder v3.0.0
+
+**Release Date**: October 19, 2025
+
+### Summary
+Major infrastructure upgrade: migrated to Parquet data format with comprehensive performance improvements, combo tag support, simplified data management, and instant setup via GitHub downloads.
+
+### What's New
+- **Instant Setup** - Download pre-tagged card database from GitHub instead of 15-20 minute initial build
+- **Parquet Migration** - Unified `all_cards.parquet` replaces multiple CSV files for faster, more efficient card storage
+- **Combo Tags** - 226 cards now tagged with combo-enabling abilities for better synergy detection
+- **Parallel Tagging** - Optional 4.2x speedup for card tagging (22s → 5.2s)
+- **Automatic Deduplication** - No more duplicate card printings cluttering your deck options
+- **Built-in Commander Filtering** - Instant identification of 2,751 commanders and 31 backgrounds
+
+### Improvements
+- **First-Run Experience** - Auto-downloads pre-tagged data on first run (seconds vs. 15-20 minutes)
+- **Faster Startup** - Binary columnar format loads significantly faster than text parsing
+- **Smaller File Sizes** - Single Parquet file is more compact than multiple CSVs
+- **Better Data Quality** - Automatic validation, deduplication, and type checking
+- **Cleaner Organization** - Single source of truth for all 29,857 cards
+- **Web Performance** - Card browser, commander catalog, and owned cards all benefit from faster data access
+- **Weekly Updates** - Pre-tagged data refreshed weekly via GitHub Actions
+
+### For Users
+Everything works the same or better! Main visible differences:
+- **First-time users**: Setup completes in seconds (auto-downloads pre-tagged data)
+- Faster load times and data operations
+- Better card recommendations with combo tag support
+- More reliable data handling
+- Web UI includes manual "Download from GitHub" button for instant refresh
+
+### Technical Details
+- Data stored in `card_files/processed/all_cards.parquet`
+- Boolean flags (`isCommander`, `isBackground`) replace separate CSV files
+- CLI execution: `python -m code.main`
+- Headless execution: `python -m code.headless_runner --config <path>`
+- GitHub Actions and Docker builds updated for Parquet workflow
+
+### Breaking Changes
+- **MAJOR**: CSV-based card data deprecated in favor of Parquet format
+- Existing CSV workflows require migration to use processed Parquet files
+- Module imports updated - use `python -m code.main` for CLI execution
+- Some internal APIs changed to support unified data source
+
+### Migration Guide
+For existing users:
+1. Pull latest code: `git pull`
+2. Delete old CSV files (optional): `rm csv_files/*.csv`
+3. Let auto-download fetch pre-tagged data OR run manual setup
+4. Existing decks and configs remain compatible
+
+For Docker users:
+1. Pull new image: `docker pull mwisnowski/mtg-python-deckbuilder:v3.0.0`
+2. Use updated docker-compose files (included)
+3. Volume mounts work the same
+
+### Full Changelog
+See [CHANGELOG.md](../../CHANGELOG.md#300---2025-10-19) for complete details.
+
+### Known Issues
+- None at release time
+
+### Acknowledgments
+This release represents a significant architectural improvement to support better performance and maintainability going forward. Thank you to all contributors and users who provided feedback!