Introduce a new filename_format setting and UI to control yt-dlp output templates. ConfigManager now includes a default filename_format (%(title)s_%(resolution)s.%(ext)s). The DownloadSettingsDialog exposes a text input and help text for the format and saves the value to ConfigManager. DownloadThread now accepts a filename_format argument and uses it when building output templates for single videos and playlists. YTSageApp reads the config and passes the filename format into the download thread. Added corresponding English language strings.
Update English UI strings in ytsage/languages/en.json to remove progress percentages and the repeated "Analyzing" prefix, replacing them with concise action messages (e.g., "Extracting basic info...", "Loading thumbnail..."). This makes status messages shorter and more consistent across regular and ytdlp-related entries without changing functionality.