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_lidarr_search.py

@@ -81,3 +81,30 @@ def test_last_resort_universal_search(monkeypatch):
     monkeypatch.setattr(mf, "lidarr_get", fake_get)
     hits = mf.lidarr_search("Daft Punk - Discovery", 10)
     assert hits and hits[0].album == "Discovery"
+
+
+def test_unreachable_lidarr_warns_loudly(monkeypatch, capsys):
+    # A connection error must surface on stderr (not silent dbg) so the
+    # YouTube fallback isn't mistaken for "Lidarr had no match".
+    monkeypatch.setattr(mf, "API_KEY", "testkey")
+    monkeypatch.setattr(mf, "DEBUG", False)
+
+    def boom(path, params=None, timeout=15):
+        raise mf.ReqConnectionError("Name or service not known")
+    monkeypatch.setattr(mf, "lidarr_get", boom)
+
+    hits = mf._lidarr_album_candidates("anything")
+    assert hits == []
+    assert "Lidarr unreachable" in capsys.readouterr().err
+
+
+def test_http_error_stays_quiet(monkeypatch, capsys):
+    monkeypatch.setattr(mf, "API_KEY", "testkey")
+    monkeypatch.setattr(mf, "DEBUG", False)
+
+    def boom(path, params=None, timeout=15):
+        raise mf.RequestException("500 Server Error")
+    monkeypatch.setattr(mf, "lidarr_get", boom)
+
+    assert mf._lidarr_album_candidates("anything") == []
+    assert "Lidarr unreachable" not in capsys.readouterr().err