fix(backend): Live-Mitschnitte aus der Suche ausschliessen

is_live meint nur "laeuft gerade als Stream" — eine Konzert-AUFNAHME kam
ungehindert durch und landete als Albumtrack in der Bibliothek ("Dat Adam - Ufo
Video Days 2015 Live" auf dem echten Kuenstlerkanal, Dauer im Fenster). Der
Variantenfilter bekommt daher eine live-Regel. Sie schaltet sich ab, wenn der
gesuchte Titel selbst live enthaelt; die Pruefung nutzt \blive\b statt includes,
sonst wuerde "deliver" die Regel aushebeln. Drei Tests dazu.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -103,6 +103,13 @@ On the deploy host the music lives at `/opt/navidrome/music`.
   next to a qualifier** ("… - 2020 Remaster") is dropped again — it sits on the release but never in
   the YouTube title, so requiring it would reject the correct upload. A title that IS a year ("1999",
   "Berlin 2020") keeps it. Unit-tested in `backend/test/ytdlp.test.js`.
+- **Live recordings are excluded by title, not by `is_live`.** `!is_live` only means "not a running
+  stream" — a concert RECORDING passes it. On the artist's own channel nothing else distinguishes it
+  from the studio track, which is how "Dat Adam - Ufo Video Days 2015 Live" (channel `Dat Adam`,
+  209 s, title contains UFO) got saved as the album track. `buildVariantFilter` therefore carries a
+  `live` rule like remix/cover/…. It self-disables when the searched title itself says live, so
+  "Live Forever" or a deliberately requested live version still works — that check uses a `\blive\b`
+  regex (`skipRe`), because a plain substring test would let "deliver"/"delivery" switch the rule off.
 - **Size cap:** `--max-filesize 30M` on every yt-dlp call; Mittelweg steps also cap at 2×
   expected duration. Prevents saving a 28-min video (52 MB) when the wrong result slips through.
 - **Leading aesthetic characters:** artists often style their name with leading punctuation