fix: reliable YouTube tagging, loud Lidarr failures, deno runtime, repair recovery

Root cause of bad album/title tags: yt-dlp's --parse-metadata reads a
single-word FROM (matching field_to_template's ^[a-zA-Z_]+$) as a *field
name*, so literal one-word titles/albums like "Cochise" became "NA". Inject
literals via seed-then-replace into meta_<tag> instead (--parse-metadata to
create the field, --replace-in-metadata with literal args to set it), which
is immune to template parsing and also creates tags the source lacks.

- yt_download: literal-safe meta_artist/title/album; hit album no longer
  clobbered by the Unknown-Album default; artist tag now created when missing.
- lidarr_search: connection/timeout errors surface via err() ("Lidarr
  unreachable … falling back to YouTube") instead of silent dbg(), so the
  YouTube fallback isn't mistaken for "no Lidarr match".
- Dockerfile: install deno (arch-aware) — the JS runtime yt-dlp needs for
  YouTube; without it: "No supported JavaScript runtime" / HTTP 403.
- repair: treat NA/Unknown placeholders as bogus and overwrite title/artist
  from source (was fill-missing-only); normalise literal "NA" album to
  "Unknown Album"; rename bogus "NA [<id>]" filenames to the recovered title.
- README updated; .gitignore excludes server/log.txt.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_playlist.py

@@ -110,3 +110,25 @@ def test_yt_download_always_sets_album_default(monkeypatch):
     monkeypatch.setattr(mf.subprocess, "run", lambda cmd, **k: captured.update(cmd=cmd) or _CP(""))
     mf.yt_download("u", "/tmp/x", "best", False)
     assert "%(album|Unknown Album)s:%(meta_album)s" in captured["cmd"]
+
+
+def test_yt_download_single_word_tags_injected_literally(monkeypatch):
+    # Regression: `--parse-metadata "Cochise:%(title)s"` makes yt-dlp treat the
+    # bare word 'Cochise' as a FIELD name (field_to_template's r'[a-zA-Z_]+$'),
+    # producing 'NA'. Single-word album/title must reach yt-dlp as literals.
+    captured = {}
+    monkeypatch.setattr(mf.os, "makedirs", lambda *a, **k: None)
+    monkeypatch.setattr(mf.subprocess, "run", lambda cmd, **k: captured.update(cmd=cmd) or _CP(""))
+    hit = mf.Hit(source="youtube", kind="track", title="Cochise",
+                 artist="Audioslave", album="Solid", payload={"videoId": "x"})
+    mf.yt_download("u", "/tmp/x", "best", False, hit=hit)
+    cmd = captured["cmd"]
+    joined = " ".join(cmd)
+    # The buggy bare-word parse-metadata FROM must be gone.
+    assert "Solid:%(album)s" not in joined
+    assert "Cochise:%(title)s" not in joined
+    # Literal values must be passed as literal args (immune to template parsing).
+    assert "Solid" in cmd
+    assert "Cochise" in cmd
+    # A hit album must not be clobbered by the Unknown-Album default.
+    assert "%(album|Unknown Album)s:%(meta_album)s" not in cmd