Complete architecture simplification: 54+ files → 37 files

- Removed 11 duplicate router files (auth.py, users.py, decks.py, card_router.py, interactions.py, user_data.py, rooms.py, games/router.py, refresh.py, card_import.py, ws.py)
- Removed duplicate core files (logging_config.py, settings.py)
- Removed unused services (card_mirror_service.py, mtgjson_loader.py, mtgjson_uploader.py)
- Removed unused schemas (proto_messages.py, protocol_constants.py)
- Created run.py startup script for simple execution
- Created app/core/config.py for unified configuration management
- Created app/core/logging.py for logging configuration
- Consolidated routers into 6 focused files (auth_router.py, users_router.py, decks_router.py, cards_router.py, user_data_router.py, games_router.py)
- Updated all imports to use consolidated model paths
- Added backward compatibility aliases in database.py
- Created SIMPLIFICATION_SUMMARY.md documentation

Architecture improvements:
- Single unified database engine with auto-detection (SQLite/PostgreSQL)
- Consolidated models into 2 files (models.py, mtg_models.py)
- Clean router structure with one file per domain
- Simplified configuration with sensible defaults
- SQLite by default for development, PostgreSQL for production

Testing:
- All imports verified working
- App loads successfully
- Ready for development and testing

backend/app/routers/__init__.py

@@ -3,29 +3,27 @@ Router package exports.
 
 All routers are mounted in app/main.py.
 This package provides centralized access to all router modules.
+
+## Consolidated Routers (Phase 3 Simplification)
+- auth_router.py - Authentication endpoints
+- users_router.py - User management + admin operations
+- decks_router.py - Deck building and management
+- cards_router.py - Card data search and interactions
+- user_data_router.py - User data, sessions, and card imports
+- games_router.py - Room management, games, and MTGJSON refresh
 """
-from app.routers import auth
-from app.routers import users
-from app.routers import decks
-from app.routers import rooms
-from app.routers import games
-from app.routers import admin
-from app.routers import card_router
-from app.routers import interactions
-from app.routers import refresh
-from app.routers import card_import
-from app.routers import user_data
+from app.routers import auth_router
+from app.routers import users_router
+from app.routers import decks_router
+from app.routers import cards_router
+from app.routers import user_data_router
+from app.routers import games_router
 
 __all__ = [
-    "auth",
-    "users",
-    "decks",
-    "rooms",
-    "games",
-    "admin",
-    "card_router",
-    "interactions",
-    "refresh",
-    "card_import",
-    "user_data",
+    "auth_router",
+    "users_router",
+    "decks_router",
+    "cards_router",
+    "user_data_router",
+    "games_router",
 ]