feat: add image opacity, config migration, settings

Add image overlay opacity support and related UI/settings, plus robust config migration and error handling.

Key changes:
- UI: image overlay now uses QGraphicsOpacityEffect, hides when disabled, and updates opacity on state changes (src/interface/dialogs/image.py).
- New NotificationPopup dialog for user alerts (src/interface/dialogs/notificationpopup.py).
- Settings dialog: added Image Opacity control, adjusted labels, persist/rollback behavior on cancel, and include opacity when saving (src/interface/dialogs/settings.py).
- State: added properties for image_opacity and image_enabled with change notifications; renamed image_width setter param for clarity (src/utils/data/state.py).
- Config: switch from config.yml to config.ini, implement one-time migration, typed read/write of values, validation/error handling, automatic backups of corrupted files and user notification (src/utils/config/config.py).
- Settings save: accept and persist image_opacity (src/utils/config/settings.py).
- Startup: initialize QApplication earlier and pass app to run_gui (src/main.py).
- Minor: removed an extra blank line in log handler and small import cleanups.

These changes enable adjustable overlay transparency, improve config reliability, and surface errors to users while preserving/backuping old configs.

src/utils/config/settings.py

@@ -5,7 +5,7 @@ from utils.data.state import state
 
 
 
-def save_settings(close=lambda: None, apiurl=None, download_path=None, down_speed_limit=None, up_speed_limit=None, image_path=None, autoresume=None, max_connections=None, max_downloads=None, bound_interface=None, image_width=None, image_offset=None):
+def save_settings(close=lambda: None, apiurl=None, download_path=None, down_speed_limit=None, up_speed_limit=None, image_path=None, autoresume=None, max_connections=None, max_downloads=None, bound_interface=None, image_width=None, image_offset=None, image_opacity=None):
     if apiurl is not None:
         state.api_url = apiurl
     if download_path is not None:
@@ -28,6 +28,8 @@ def save_settings(close=lambda: None, apiurl=None, download_path=None, down_spee
         state.image_width = image_width
     if image_offset is not None:
         state.image_offset = image_offset
+    if image_opacity is not None: 
+        state.image_opacity = image_opacity
 
     update_settings() # Update LibTorrent Session Settings
     consoleLog("Saved Settings")