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/mirror_models.py

@@ -11,7 +11,6 @@ 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):
@@ -25,7 +24,12 @@ class MtgCardMirror(Base):
     __tablename__ = "mtg_cards_mirror"
 
     id = Column(Integer, primary_key=True, index=True)
-    source_id = Column(Integer, nullable=True, index=True)  # References mtg_cards.id
+    source_id = Column(
+        Integer, 
+        nullable=True, 
+        index=True,
+        comment="Logical reference to mtg_cards.id in mtg_data database (cross-DB reference, no FK constraint)"
+    )
     name = Column(String(255), nullable=False, index=True)
     mana_cost = Column(String(255), nullable=True)
     type_line = Column(String(255), nullable=True)
@@ -91,14 +95,3 @@ class DeckCardLink(Base):
             f"<DeckCardLink deck={self.deck_id} card={self.card_id} "
             f"qty={self.quantity} zone={self.zone}>"
         )
-
-
-# Add back-references to existing models
-from app.models.models import DecklistFile
-
-DecklistFile.card_links = relationship(
-    "DeckCardLink",
-    back_populates="deck",
-    cascade="all, delete-orphan",
-    order_by="DeckCardLink.id"
-)