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/app/models/__init__.py

@@ -11,6 +11,11 @@ from app.models.user_data import (
 from app.models.user_deck import UserDeck, UserDeckCard, DeckPrecedent, DeckPrecedentCard, CardSuggestion
 from app.models.card_import_batch import CardImportBatch
 from app.models.user_card_import_record import UserCardImportRecord
+from app.models.user_card_import import UserCardImport
+
+# Import relationships LAST to avoid circular imports
+# This defines cross-model references (e.g., DecklistFile.card_links)
+from app.models import relationships
 
 __all__ = [
     "User",
@@ -47,4 +52,5 @@ __all__ = [
     "CardSuggestion",
     "CardImportBatch",
     "UserCardImportRecord",
+    "UserCardImport",
 ]