Bookmark Manager, History Manager, Search/Find, and UI Improvements
- Added full Bookmark Manager with folders (Default, Favorites, Reading List + custom), duplicate detection, multi-select delete, and persistent notes.
- Added History Manager with date filtering, URL normalization, multi-select delete, and search by title/URL.
- Added Dashboard search (cards) and WebView find-in-page (case insensitive, real-time).
- Fixed YouTube SPA navigation – history now records internal video navigation with 1.5s delay.
- Added History/Bookmarks enable/disable toggle with QSettings persistence.
- Added dark theme support for all dialogs and form fields.
- Added sandwich menu with quick access to all features.
- Window hides on close (reopen via menu).
- Fixed multi-delete crashes and duplicate connections.
- Fixed custom folders and comments not persisting.
