Fix 7 bugs: bounds checks, deepcopy, time import, JS keys, unused import

- Add bounds check on src_batch index in add_from_source and copy_source
- Guard delete callback against stale index after rapid clicks
- Replace __import__('time').time() with time.time() in sync_to_db
- Use deepcopy(DEFAULTS) consistently in utils.py and main.py
- Use JSON.stringify in JS onConfigure fallback path for key storage
- Read state.show_comfy_monitor for checkbox initial value
- Remove unused KEY_BATCH_DATA import from tab_projects_ng

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tab_projects_ng.py

@@ -7,7 +7,7 @@ from nicegui import ui
 
 from state import AppState
 from db import ProjectDB
-from utils import save_config, sync_to_db, KEY_BATCH_DATA
+from utils import save_config, sync_to_db
 
 logger = logging.getLogger(__name__)