Install Node.js via nodeenv (pip); use web client

nodeenv is a Python package that downloads a pre-built Node.js binary —
no apt repos, no compilation, guaranteed to work in python:3.12-slim.
The 'node' binary is linked into /usr/local/bin so yt-dlp can find it.

With Node.js available the web client works fully (37 formats) and can
solve YouTube's n-challenge that every other approach was failing on.

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

backend/Dockerfile

@@ -6,6 +6,13 @@ RUN apt-get update && apt-get install -y ffmpeg gosu && rm -rf /var/lib/apt/list
 
 COPY backend/requirements.txt ./backend/requirements.txt
 RUN pip install --no-cache-dir -r backend/requirements.txt && pip install --no-cache-dir -U yt-dlp
+
+# nodeenv downloads a pre-built Node.js binary via pip — no apt repos needed.
+# yt-dlp needs 'node' in PATH to solve YouTube's n-challenge (JS obfuscation).
+RUN pip install --no-cache-dir nodeenv && \
+    nodeenv --prebuilt /opt/node && \
+    ln -sf /opt/node/bin/node /usr/local/bin/node
+
 RUN echo "--cache-dir /data/yt-dlp-cache" > /etc/yt-dlp.conf
 
 COPY backend/ ./backend/

backend/routers/settings.py

@@ -247,7 +247,7 @@ def ytdlp_test(
             "yt-dlp",
             "https://www.youtube.com/watch?v=dQw4w9WgXcQ",
             "--dump-json", "--no-download", "--no-playlist",
-            "--extractor-args", "youtube:player_client=web_embedded",
+            "--extractor-args", "youtube:player_client=web",
             *cookie_args,
         ],
         capture_output=True, text=True, timeout=30,

backend/services/ytdlp.py

@@ -216,7 +216,7 @@ def fetch_video_metadata(video_id: str) -> dict | None:
     base_cmd = [
         "yt-dlp", url,
         "--dump-json", "--no-download", "--no-playlist",
-        "--extractor-args", "youtube:player_client=web_embedded",
+        "--extractor-args", "youtube:player_client=web",
     ]
     stdout, stderr, code = _run([*base_cmd, *cookie_args], timeout=30)
     if code != 0:
@@ -567,7 +567,7 @@ def start_download(
                     "--no-part", "--no-mtime",
                     "-o", output_template,
                     "--newline", "--progress", "--no-colors",
-                    "--extractor-args", "youtube:player_client=web_embedded",
+                    "--extractor-args", "youtube:player_client=web",
                     *cookie_args,
                 ],
                 stdout=subprocess.PIPE,