Adjusted padding, margin, and spacing for a more compact layout. Standardized the thumbnail size to 240x135 (16:9 ratio) and reduced the menu button size for better visual balance.
Refactors the history loading process to emit entries as soon as they are loaded, allowing the UI to display immediately. Thumbnail downloads are now handled in the background, with widgets updated via a new signal when thumbnails are cached. This prevents UI freezes and improves responsiveness by showing placeholders until thumbnails are available.
Introduces a HistoryLoaderThread to load history entries and pre-fetch thumbnails in the background, preventing UI freezes. Adds a loading spinner and disables the 'Clear All' button while loading, improving user experience during history retrieval.
Introduces a download history dialog with thumbnail previews, redownload, and remove options. Updates all language files to support history-related UI strings. Adds HistoryManager utility and integrates history dialog into the main GUI. Enhances downloader to better track final downloaded files and merged outputs.
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