Phase 3: Schema Layer - Pydantic v2 migration, deduplication, and missing schemas

- Migrated all schemas to Pydantic v2 syntax (model_config, ConfigDict)
- Fixed mutable default in ProtoMessageBase using Field(default_factory=datetime.now)
- Consolidated CardCollection and Wishlist schemas in user_card_collection.py
- Created game_schemas.py with GameCreate, GameResponse, GameJoinRequest, etc.
- Created mtg_card_schemas.py with MtgCardResponse, MtgCardSearchRequest, etc.
- Added CardImportBatchCreate, CardImportBatchResponse, UserCardImportCreate/Response schemas
- Fixed duplicate UserCardImportRecord class between card_import_batch.py and user_card_import_record.py
- Updated __init__.py with comprehensive schema exports
- Created verify_schemas.py for schema-model matching verification

backend/alembic/versions/001_initial_user_schema.py

@@ -138,8 +138,7 @@ def upgrade() -> None:
         sa.Column('created_at', sa.DateTime(), server_default=sa.func.now()),
         sa.Column('updated_at', sa.DateTime(), server_default=sa.func.now(), onupdate=sa.func.now()),
     )
-    op.create_index('idx_collection_user', 'user_card_collection', ['user_id'])
-    op.create_index('idx_collection_card', 'user_card_collection', ['card_id'])
+    op.create_index('idx_collection_user_card', 'user_card_collection', ['user_id', 'card_id'])
     op.create_unique_constraint('uq_collection_unique', 'user_card_collection', ['user_id', 'card_id', 'is_foil', 'is_alt_art'])
 
     # 9. Card Wishlist Table