Fix: [2.0.4] 쿠키 read-only 마운트 및 포맷 에러 해결

- 쿠키 파일을 임시 파일에 복사하여 yt-dlp 쓰기 가능하도록 처리
- format: worst 추가하여 포맷 선택 에러 방지

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

app/transcript.py

@@ -1,6 +1,12 @@
+import os
+import shutil
+import tempfile
+
 import httpx
 import yt_dlp
 
+COOKIES_SRC = "/app/cookies.txt"
+
 
 def extract_video_id(url: str) -> str:
     """YouTube URL에서 video ID 추출."""
@@ -20,13 +26,22 @@ def fetch_transcript(video_id: str) -> str:
         "writeautomaticsub": True,
         "subtitleslangs": ["ko", "en"],
         "subtitlesformat": "json3",
+        "format": "worst",
         "quiet": True,
         "no_warnings": True,
-        "cookiefile": "/app/cookies.txt",
     }
 
-    with yt_dlp.YoutubeDL(ydl_opts) as ydl:
-        info = ydl.extract_info(url, download=False)
+    if os.path.isfile(COOKIES_SRC):
+        tmp = tempfile.NamedTemporaryFile(delete=False, suffix=".txt")
+        shutil.copy2(COOKIES_SRC, tmp.name)
+        ydl_opts["cookiefile"] = tmp.name
+
+    try:
+        with yt_dlp.YoutubeDL(ydl_opts) as ydl:
+            info = ydl.extract_info(url, download=False)
+    finally:
+        if "cookiefile" in ydl_opts:
+            os.unlink(ydl_opts["cookiefile"])
 
     subs = info.get("automatic_captions", {})
     lang = "ko" if "ko" in subs else "en" if "en" in subs else None