feat: migrate to unified Parquet format with instant GitHub setup and 4x faster tagging

RELEASE_NOTES_TEMPLATE.md

@@ -1,16 +1,36 @@
 # MTG Python Deckbuilder ${VERSION}
 
 ### Summary
-_No unreleased changes yet_
+Major infrastructure upgrade: migrated to Parquet data format with comprehensive performance improvements, combo tag support, simplified data management, and instant setup via GitHub downloads.
 
-### Added
-_None_
+### 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
 
-### Changed
-_None_
+### 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
 
-### Removed
-_None_
+### 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
 
-### Fixed
-_None_
+### 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