Add node symlink to Dockerfile; expand ytdlp-test diagnostics

Debian installs nodejs as /usr/bin/nodejs but yt-dlp looks for 'node'.
The symlink ensures yt-dlp can find the runtime.

Diagnostics now report node path/version and yt-dlp version so we can
verify the environment without shelling into the container.

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

backend/Dockerfile

@@ -2,7 +2,9 @@ FROM python:3.12-slim
 
 WORKDIR /app
 
-RUN apt-get update && apt-get install -y ffmpeg gosu nodejs && rm -rf /var/lib/apt/lists/*
+RUN apt-get update && apt-get install -y ffmpeg gosu nodejs && \
+    ln -sf /usr/bin/nodejs /usr/bin/node && \
+    rm -rf /var/lib/apt/lists/*
 
 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

backend/routers/settings.py

@@ -222,9 +222,26 @@ def oauth2_disable(
 def ytdlp_test(
     current_user: User = Depends(get_current_user),
 ):
-    """Run a quick yt-dlp metadata fetch on a public video and return raw output for diagnostics."""
-    import subprocess
+    """Run a quick yt-dlp metadata fetch and environment check for diagnostics."""
+    import subprocess, shutil
     cookie_args = ytdlp._cookie_args()
+
+    node_path = shutil.which("node") or shutil.which("nodejs")
+    node_version = None
+    if node_path:
+        try:
+            nv = subprocess.run([node_path, "--version"], capture_output=True, text=True, timeout=5)
+            node_version = nv.stdout.strip()
+        except Exception:
+            pass
+
+    yt_version = None
+    try:
+        yv = subprocess.run(["yt-dlp", "--version"], capture_output=True, text=True, timeout=5)
+        yt_version = yv.stdout.strip()
+    except Exception:
+        pass
+
     result = subprocess.run(
         [
             "yt-dlp",
@@ -236,8 +253,11 @@ def ytdlp_test(
         capture_output=True, text=True, timeout=30,
     )
     return {
-        "returncode": result.returncode,
+        "node_path": node_path,
+        "node_version": node_version,
+        "yt_dlp_version": yt_version,
         "cookie_args": cookie_args,
+        "returncode": result.returncode,
         "stdout_lines": result.stdout.splitlines()[:5],
         "stderr_tail": result.stderr.splitlines()[-20:],
         "success": result.returncode == 0,