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>

README.md

@@ -131,9 +131,11 @@ file using the `[id]` in its filename, and fixes tags. Useful when downloads lan
 missing album or wrong year.
 
 It is deliberately **conservative**: it overwrites **album** and **year** (the usual
-breakage), but only *fills in* a missing **artist**/**title** — it never overwrites existing
-artist/title with channel names or decorated video titles. Files whose source returns no real
-music metadata (no album and no release year — e.g. plain music videos) are left untouched.
+breakage), and fills in **artist**/**title** when they are missing *or* a known-bogus
+placeholder (`NA`, `Unknown Album`, `Unknown Artist` — left behind by older buggy tagging) —
+but it never overwrites a genuine existing artist/title with a channel name or decorated video
+title. A bogus `NA [<id>].<ext>` filename is renamed to the recovered title, and a literal
+`NA` album with no source album is normalised to `Unknown Album`.
 
 It re-queries the source over the network, so run it occasionally, not constantly. Requires
 `mutagen` (a yt-dlp dependency, usually already present). CLI-only — not exposed via the REST API.