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/models.py

@@ -45,6 +45,45 @@ class User(Base):
         return f"<User {self.username} (ID: {self.id})>"
 
 
+class MtgonlineCard(Base):
+    """
+    Local card data mirror for the mtgonline database.
+    
+    Mirrors data from mtg_cards (mtgdata database) to avoid cross-database
+    joins during deckbuilding. Maintains source_id to reference the canonical
+    mtg_cards.id for sync tracking.
+    """
+    __tablename__ = "mtgonline_cards"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    source_id = Column(Integer, nullable=True, index=True)  # References mtg_cards.id in mtgdata
+    name = Column(String(255), nullable=False, index=True)
+    mana_cost = Column(String(255), nullable=True)
+    type_line = Column(String(255), nullable=True)
+    oracle_text = Column(Text, nullable=True)
+    power = Column(String(50), nullable=True)
+    toughness = Column(String(50), nullable=True)
+    rarity = Column(String(50), nullable=True)
+    layout = Column(String(50), nullable=True)
+    artist = Column(String(255), nullable=True)
+    flavor_text = Column(Text, nullable=True)
+    numbers = Column(String(100), nullable=True)
+    identifiers = Column(Text, nullable=True)  # JSON string
+    images = Column(Text, nullable=True)  # JSON string
+    image = Column(Text, nullable=True)  # Card image URL
+    set_code = Column(String(10), nullable=True, index=True)
+    set_name = Column(String(255), nullable=True)
+    card_parts = Column(Text, nullable=True)  # Comma-separated face names
+    keywords = Column(Text, nullable=True)  # Comma-separated keywords
+    legalities = Column(Text, nullable=True)  # JSON of format legality
+    # Sync tracking
+    synced_at = Column(DateTime, server_default=func.now(), onupdate=func.now())
+    created_at = Column(DateTime, server_default=func.now())
+    
+    def __repr__(self) -> str:
+        return f"<MtonlineCard {self.name} (ID: {self.id}, source: {self.source_id})>"
+
+
 class DecklistFolder(Base):
     """User deck folder."""
     __tablename__ = "mtgonline_decklist_folders"