feat: MTG database integration with Redis caching

- Added MTG card ORM models (mtg_cards, mtg_sets tables)
- Created card_database service with search, get_by_name, get_by_set
- Added Redis client with caching layer (3600s TTL default)
- Created card router with caching on all endpoints:
  - Search cards (5min cache)
  - Get card by name (10min cache)
  - Get cards by set (15min cache)
  - Get card types/rarities (30min cache)
  - Get sets (1hr cache)
  - Get statistics (1hr cache)
- Updated settings.py:
  - Added JWT_SECRET_KEY field
  - Added DB_CONFIG and REDIS_CONFIG dictionaries
- Updated security.py to use JWT_SECRET_KEY with fallback
- Updated auth.py to use timezone-aware datetimes
- Updated refresh_mtg.py to use settings instead of os.environ
- Updated mtg_monitor.py to use settings for connections
- Added services package with __init__.py

All 20 tests passing.

backend/app/core/database.py

@@ -2,6 +2,7 @@
 Database engine and session management.
 
 Provides async SQLAlchemy engine and session factory for dependency injection.
+Supports dual database connections for cockatrice app and mtgjson data.
 """
 from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
 from sqlalchemy.orm import DeclarativeBase
@@ -9,6 +10,7 @@ from app.core.settings import get_settings
 
 settings = get_settings()
 
+# Primary database engine (cockatrice app)
 engine = create_async_engine(
     settings.DATABASE_URL,
     echo=settings.DEBUG,
@@ -23,17 +25,32 @@ async_session = async_sessionmaker(
     expire_on_commit=False,
 )
 
+# Secondary database engine (mtgjson data)
+mtg_engine = create_async_engine(
+    settings.MTG_DATABASE_URL,
+    echo=settings.DEBUG,
+    pool_pre_ping=True,
+    pool_size=10,
+    max_overflow=5,
+)
+
+mtg_async_session = async_sessionmaker(
+    mtg_engine,
+    class_=AsyncSession,
+    expire_on_commit=False,
+)
+
 
 class Base(DeclarativeBase):
     """Base class for all ORM models."""
     pass
 
 
-__all__ = ["Base", "get_db", "async_session", "engine"]
+__all__ = ["Base", "get_db", "async_session", "engine", "mtg_get_db", "mtg_async_session", "mtg_engine"]
 
 
 async def get_db() -> AsyncSession:
-    """FastAPI dependency that provides a database session."""
+    """FastAPI dependency that provides a database session for the cockatrice app."""
     async with async_session() as session:
         try:
             yield session
@@ -43,3 +60,16 @@ async def get_db() -> AsyncSession:
             raise
         finally:
             await session.close()
+
+
+async def mtg_get_db() -> AsyncSession:
+    """FastAPI dependency that provides a database session for mtgjson data."""
+    async with mtg_async_session() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+        finally:
+            await session.close()