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/alembic/versions/003_mtgonline_cards_table.py

@@ -0,0 +1,55 @@
+"""Add mtgonline_cards table for local card data mirror
+
+Revision ID: 003
+Revises: 002
+Create Date: 2026-07-23 00:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '003'
+down_revision: Union[str, None] = '002'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Create mtgonline_cards table for local card data mirror."""
+    op.create_table(
+        'mtgonline_cards',
+        sa.Column('id', sa.Integer(), primary_key=True, autoincrement=True),
+        sa.Column('source_id', sa.Integer(), nullable=True, index=True),  # References mtg_cards.id in mtgdata
+        sa.Column('name', sa.String(255), nullable=False, index=True),
+        sa.Column('mana_cost', sa.String(255), nullable=True),
+        sa.Column('type_line', sa.String(255), nullable=True),
+        sa.Column('oracle_text', sa.Text(), nullable=True),
+        sa.Column('power', sa.String(50), nullable=True),
+        sa.Column('toughness', sa.String(50), nullable=True),
+        sa.Column('rarity', sa.String(50), nullable=True),
+        sa.Column('layout', sa.String(50), nullable=True),
+        sa.Column('artist', sa.String(255), nullable=True),
+        sa.Column('flavor_text', sa.Text(), nullable=True),
+        sa.Column('numbers', sa.String(100), nullable=True),
+        sa.Column('identifiers', sa.Text(), nullable=True),  # JSON string
+        sa.Column('images', sa.Text(), nullable=True),  # JSON string
+        sa.Column('image', sa.Text(), nullable=True),  # Card image URL
+        sa.Column('set_code', sa.String(10), nullable=True, index=True),
+        sa.Column('set_name', sa.String(255), nullable=True),
+        sa.Column('card_parts', sa.Text(), nullable=True),  # Comma-separated face names
+        sa.Column('keywords', sa.Text(), nullable=True),  # Comma-separated keywords
+        sa.Column('legalities', sa.Text(), nullable=True),  # JSON of format legality
+        sa.Column('synced_at', sa.DateTime(), server_default=sa.func.now(), onupdate=sa.func.now()),
+        sa.Column('created_at', sa.DateTime(), server_default=sa.func.now()),
+    )
+    op.create_index('idx_mtgonline_cards_name', 'mtgonline_cards', ['name'])
+    op.create_index('idx_mtgonline_cards_set', 'mtgonline_cards', ['set_code'])
+
+
+def downgrade() -> None:
+    """Drop mtgonline_cards table."""
+    op.drop_table('mtgonline_cards')