Fix SyntaxError in ytdlp.py start_download: duplicate try block

Two back-to-back try: blocks with only one finally: caused
"expected 'except' or 'finally' block" at startup. Merged into one.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/services/ytdlp.py

@@ -908,8 +908,6 @@ def start_download(
                     stderr=subprocess.STDOUT,
                     text=True,
                 )
-
-            try:
                 file_path = None
                 stream_index = 0
                 output_lines: list[str] = []