docs: update documentation for rules engine integration

- HANDOFF.md: Added rules engine section, updated architecture diagram
- state.json: Updated project summary, files_created, files_modified, commit_hash
- README.md: Added rules engine to features and architecture
- ROADMAP.md: Added MTG Rules Engine Integration section (2.10)

README.md

@@ -13,6 +13,7 @@ This project provides a backend API for a Magic: The Gathering Online platform.
 - **Redis Caching** — Used for card lookup caching and interaction pipeline state.
 - **Card Import Feature** — Users can import their card collection (fuzzy matching enabled) for deckbuilding constraints.
 - **Deck Management** — Full deck CRUD with precedents, suggestions, and status tracking (DRAFT/FINAL).
+- **MTG Rules Engine** — Integrated in `backend/mtg_rules_engine/` for multiplayer game server (rules enforcement, card validation, keyword processing).
 - **REST API** — `/docs` (Swagger) available at runtime.
 
 ## Architecture
@@ -20,6 +21,17 @@ This project provides a backend API for a Magic: The Gathering Online platform.
 ```
 mtgonline/
 ├── backend/                  # FastAPI application
+│   ├── mtg_rules_engine/     # MTG rules engine (rules enforcement for multiplayer)
+│   │   ├── engine.py         # Core game engine
+│   │   ├── rules_engine.py   # Rules engine core
+│   │   ├── keywords.py       # Card keywords
+│   │   ├── keywords_db.py    # Keywords database
+│   │   ├── keyword_validator.py # Keyword validation
+│   │   ├── validator.py      # Card validation
+│   │   ├── updater.py        # Engine updater
+│   │   ├── update_check.py   # Update checker
+│   │   ├── test_engine.py    # Engine tests
+│   │   └── README.md         # Rules engine docs
 │   ├── app/
 │   │   ├── core/             # Settings, database engines, Redis client
 │   │   ├── models/           # SQLAlchemy ORM models (app + MTG)