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/services/__init__.py

@@ -0,0 +1,22 @@
+"""Services package."""
+from app.services.card_database import (
+    search_cards,
+    get_card_by_name,
+    get_cards_by_set,
+    get_card_types,
+    get_card_rarities,
+    get_sets,
+    get_set_by_code,
+    get_card_statistics,
+)
+
+__all__ = [
+    "search_cards",
+    "get_card_by_name",
+    "get_cards_by_set",
+    "get_card_types",
+    "get_card_rarities",
+    "get_sets",
+    "get_set_by_code",
+    "get_card_statistics",
+]