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/main.py

@@ -20,8 +20,7 @@ import signal
 import time
 import sys
 
-def run_gui():
-    app = QtWidgets.QApplication.instance() or QtWidgets.QApplication(sys.argv)
+def run_gui(app):
     qdarktheme.setup_theme("auto")
     widget = MainWindow()
     
@@ -42,7 +41,11 @@ def keyboardinterrupthandler(signum, frame):
 def main():
     # Begin counting startup time
     start_time = time.perf_counter()
-    # Parse saved files
+    
+    # Initialize UI Engine
+    app = QtWidgets.QApplication.instance() or QtWidgets.QApplication(sys.argv)
+
+    # Parse saved files 
     read_config()
     logs = get_download_logs()
     _, downloads = split_data(logs)
@@ -65,7 +68,7 @@ def main():
     elapsed = time.perf_counter() - start_time
     consoleLog(f"Initialization completed in {elapsed:.2f}s. Launching GUI")
     # Launch GUI
-    run_gui()
+    run_gui(app)
 
 if __name__ == "__main__":
     main()