feat: add YouTube cookies upload via web UI

Adds a Settings panel to upload a cookies.txt file directly from the
browser, persisted in a named Docker volume. yt-dlp uses the file
when present to bypass YouTube bot detection.

app/downloader.py

@@ -2,6 +2,7 @@ import asyncio
 import uuid
 import os
 from pathlib import Path
+from app.config import settings
 
 AUDIO_TMP_DIR = "/tmp/apoena-audio"
 
@@ -21,9 +22,13 @@ async def extract_audio(url: str) -> Path:
         "--audio-quality", "128K",
         "--format", "bestaudio/best",
         "--output", outtmpl,
-        url,
     ]
 
+    if settings.yt_dlp_cookies_file:
+        cmd += ["--cookies", settings.yt_dlp_cookies_file]
+
+    cmd.append(url)
+
     proc = await asyncio.create_subprocess_exec(
         *cmd,
         stdout=asyncio.subprocess.PIPE,