Fix SQLite autoincrement and test configuration

- Removed autoincrement=True from BigInteger primary keys (UserDeck, UserDeckCard, DeckPrecedent, etc.)
- SQLite doesn't support autoincrement on BigInteger columns
- Updated conftest.py test engine configuration
- All admin tests passing (5/5)
- All auth tests passing (7/7)
- Game model tests passing (13/13)
- Deck tests still failing due to SQLite RETURNING clause issue

backend/app/core/database.py

@@ -68,6 +68,10 @@ engine = create_async_engine(
         if not config.is_sqlite
         else {
             "pool_pre_ping": False,
+            # Disable insertmanyvalues to avoid RETURNING clause issues with aiosqlite
+            "execution_options": {
+                "insertmanyvalues_page_size": 0,
+            },
         }
     ),
 )