Add download history feature with UI and localization

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.

languages/en.json

@@ -69,6 +69,7 @@
     "run_command": "Run Command",
     "custom_command_help": "Help",
     "about": "About",
+    "history": "History",
     "analyze": "Analyze",
     "paste_url": "Paste URL",
     "select_videos": "Select Videos...",
@@ -428,5 +429,32 @@
     "copyright_blocked": "This video is blocked due to copyright claims.\nThe content owner has restricted access to this video.",
     "extraction_failed": "Failed to extract video information. This might be a temporary issue.\nPlease try again in a few minutes, or check if the video link is correct.",
     "generic_error": "Could not extract video information. Please check your link.\nTechnical details: {error}"
+  },
+  "history": {
+    "title": "Download History",
+    "clear_all": "Clear All History",
+    "clear_confirm_title": "Clear History?",
+    "clear_confirm_message": "Are you sure you want to clear all download history? This cannot be undone.",
+    "no_history": "No download history yet",
+    "no_history_description": "Your downloaded videos and audio will appear here",
+    "search_placeholder": "Search history...",
+    "open_location": "Open File Location",
+    "redownload": "Redownload",
+    "remove": "Remove from History",
+    "file_not_found": "File not found at original location",
+    "file_not_found_message": "The file was moved or deleted:\n{path}",
+    "downloaded_on": "Downloaded on {date}",
+    "file_size": "Size: {size}",
+    "audio_download": "Audio",
+    "video_download": "Video",
+    "remove_confirm_title": "Remove from History?",
+    "remove_confirm_message": "Remove this item from history?\n\n{title}",
+    "item_removed": "Item removed from history",
+    "history_cleared": "History cleared",
+    "entries_count": "{count} downloads",
+    "one_entry": "1 download",
+    "redownload_confirm_title": "Redownload Video?",
+    "redownload_confirm_message": "Download this video again using the same settings?\n\n{title}",
+    "redownload_started": "Redownload started"
   }
 }