feat: complete deckbuilding feature with local card mirror

- Add MtgonlineCard model (local card data mirror in mtgonline DB)
- Create user_deck.py models (UserDeck, UserDeckCard, DeckPrecedent, CardSuggestion)
- Create user_deck_schemas.py with Pydantic schemas
- Update decks.py router to use local MtgonlineCard instead of cross-DB MtgCard
- Add migration 002 (user deck building tables)
- Add migration 003 (mtgonline_cards table)
- All card lookups now use local mirror for fast queries
- No cross-DB joins in deckbuilding endpoints

backend/app/models/mirror_models.py

@@ -11,6 +11,7 @@ from sqlalchemy import (
 from sqlalchemy.orm import relationship
 from sqlalchemy.sql import func
 from app.core.database import Base
+from app.models.models import DecklistFile
 
 
 class MtgCardMirror(Base):