Add configurable output filename format

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.

ytsage/core/ytsage_downloader.py

@@ -72,6 +72,7 @@ class DownloadThread(QThread):
         preferred_output_format="mp4",
         force_audio_format=False,
         preferred_audio_format="best",
+        filename_format=None,
     ) -> None:
         super().__init__()
         self.url = url
@@ -99,6 +100,7 @@ class DownloadThread(QThread):
         self.preferred_output_format = preferred_output_format
         self.force_audio_format = force_audio_format
         self.preferred_audio_format = preferred_audio_format
+        self.filename_format = filename_format
         self.paused: bool = False
         self.cancelled: bool = False
         self.process: Optional[subprocess.Popen] = None
@@ -274,11 +276,14 @@ class DownloadThread(QThread):
         # Use string concatenation instead of Path.joinpath to avoid Path object issues
         base_path: str = self.path.as_posix()
         
+        # Determine the filename part of the template
+        filename_part = self.filename_format if self.filename_format else "%(title)s_%(resolution)s.%(ext)s"
+
         if self.is_playlist:
             # Create output template with playlist subfolder
-            output_template: str = f"{base_path}/%(playlist_title)s/%(title)s_%(resolution)s.%(ext)s"
+            output_template: str = f"{base_path}/%(playlist_title)s/{filename_part}"
         else:
-            output_template: str = f"{base_path}/%(title)s_%(resolution)s.%(ext)s"
+            output_template: str = f"{base_path}/{filename_part}"
 
         cmd.extend(["-o", str(output_template)])