Add output format selection to settings

Introduces new settings for forcing output format when merging videos, allowing users to select a preferred format (mp4, webm, mkv). Updates all language files with relevant translations, adds UI controls in the settings dialog, persists settings via ConfigManager, and passes options through the download workflow to yt-dlp.

src/utils/ytsage_config_manager.py

@@ -80,6 +80,8 @@ class ConfigManager:
         "auto_update_frequency": "daily",
         "last_update_check": 0,
         "language": "en",
+        "force_output_format": False,
+        "preferred_output_format": "mp4",
         "cached_versions": {
             "ytdlp": {"version": None, "path": None, "last_check": 0, "path_mtime": 0},
             "ffmpeg": {"version": None, "path": None, "last_check": 0, "path_mtime": 0},