fix: Update subtitle download error handling to return unknown title

summarize_yt/cli.py

@@ -108,7 +108,7 @@ def download_subtitles(url: str, quiet: bool = False) -> tuple[bool, Path | None
 
         if not vtt_files:
             print("No VTT file found after download", file=sys.stderr)
-            return False, None, 0
+            return False, None, 0, "Unknown Title"
 
         return True, vtt_files[0], duration_mins, title
 
@@ -119,7 +119,7 @@ def download_subtitles(url: str, quiet: bool = False) -> tuple[bool, Path | None
             import traceback
 
             traceback.print_exc()
-        return False, None, 0
+        return False, None, 0, "Unknown Title"
 
 
 def clean_vtt_text(text: str) -> str: