Added a simple Logo, PWA functionality, dark theme, search and IP based currency preferences.

[SubhanRaj]

This pull request introduces a major feature upgrade by adding Progressive Web App (PWA) support to the SubGrid app. It also implements a comprehensive search/filter functionality for subscriptions across all views, improves dark mode styling, and enhances user interactions with clearer feedback and confirmation dialogs. The changes are documented in a new PWA.md guide and referenced in the main README.md.

PWA Implementation

• Added a full-featured PWA with offline support, installability, service worker caching, manifest, and long-term device storage. All details and usage instructions are documented in the new PWA.md file.
• Updated README.md to announce PWA support and link to documentation, highlighting key benefits and features.

Search & Filter Functionality

• Implemented search and filter for subscriptions in the main list and grid views, including UI feedback for empty search results. Search works by name, cycle, price, or currency and updates all visualization views accordingly.

Dark Mode & UI Improvements

• Enhanced dark mode styling for buttons, subscription list items, and preset grid elements to ensure consistent appearance across light and dark themes.

User Experience Enhancements

• Improved the "Clear All Subscriptions" action with a confirmation dialog and success feedback, making it safer and more user-friendly.

Codebase Organization

• Exposed key variables globally for easier access across modules and views, supporting the new search/filter logic.