Add a Reset button next to the filename format input so users can restore the default pattern. The filename input and reset button are grouped in a QHBoxLayout; the button is fixed width (70) and sets the field back to the default %(title)s_%(resolution)s.%(ext)s. Also add the corresponding i18n key (buttons.reset -> "Reset") to en.json.
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.
Moved all files from src/gui/ to ytsage/gui/ and updated import statements to use relative imports within the new package structure. This improves modularity and prepares the codebase for distribution as a proper Python package.
oop7