feat: implement personalized background image feature

- Added functionality for users to select and customize background images in settings, including predefined options and URL uploads.
- Updated `ViewPreferences` to store background image settings and modified `userPreferencesService` to handle updates.
- Enhanced global styles for improved readability with background images, including blur and transparency effects.
- Integrated `BackgroundImageSelector` component into settings for intuitive user experience.
- Refactored `Card` components across the app to use a new 'glass' variant for better aesthetics.

src/lib/types.ts

@@ -104,6 +104,9 @@ export interface ViewPreferences {
   objectivesCollapsed: boolean;
   theme: Theme;
   fontSize: 'small' | 'medium' | 'large';
+  backgroundImage?: string;
+  backgroundBlur?: number;
+  backgroundOpacity?: number;
   [key: string]:
     | boolean
     | 'tags'
@@ -112,6 +115,8 @@ export interface ViewPreferences {
     | 'small'
     | 'medium'
     | 'large'
+    | string
+    | number
     | undefined;
 }