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/schemas/game_schemas.py

@@ -0,0 +1,64 @@
+"""Pydantic schemas for game features."""
+from pydantic import BaseModel, Field, ConfigDict
+from typing import Optional, List, Dict, Any
+from datetime import datetime
+
+
+class GameCreate(BaseModel):
+    """Game creation request."""
+    room_id: int
+    game_type: Optional[str] = None
+    description: Optional[str] = None
+    password: Optional[str] = None
+    max_players: int = Field(4, ge=2, le=8)
+
+
+class GameResponse(BaseModel):
+    """Game response payload."""
+    id: int
+    room_id: int
+    game_type: Optional[str]
+    description: Optional[str]
+    with_password: bool
+    max_players: int
+    player_count: int
+    started: bool
+    creation_date: datetime
+    
+    model_config = ConfigDict(from_attributes=True)
+
+
+class GameJoinRequest(BaseModel):
+    """Game join request."""
+    game_id: int
+    password: Optional[str] = None
+
+
+class GameLeaveRequest(BaseModel):
+    """Game leave request."""
+    game_id: int
+
+
+class GameListResponse(BaseModel):
+    """List of games."""
+    games: List[GameResponse]
+    total: int
+
+
+class GamePlayerResponse(BaseModel):
+    """Game player response."""
+    user_id: int
+    username: str
+    deck_id: Optional[int] = None
+    is_ready: bool = False
+    is_host: bool = False
+
+
+class GameStateResponse(BaseModel):
+    """Game state response."""
+    game_id: int
+    players: List[GamePlayerResponse]
+    turn: int
+    phase: str
+    zones: Dict[str, Any]
+    updated_at: datetime