fix(backend): Neuauflage-Jahreszahl nicht als Pflicht-Keyword fordern

Folgekorrektur zu 02b5905: "… - 2020 Remaster" steht auf der Veroeffentlichung,
aber nie im YouTube-Titel — als Pflicht-Keyword haette die Zahl den richtigen
Upload abgelehnt. Jahreszahlen neben einem Qualifier (remaster/version/edition/
anniversary/mono/stereo) fallen daher wieder raus; ein Titel, der selbst eine
Jahreszahl ist ("1999", "Berlin 2020"), behaelt sie. Gegen 29 Beispieltitel
gemessen verhalten sich 24 exakt wie vorher.

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

CLAUDE.md

@@ -99,8 +99,10 @@ On the deploy host the music lives at `/opt/navidrome/music`.
   check, so nothing else caught it). Numeric tokens are now emitted as `\b<n>\b` in addition to the
   two longest words. Same fix carries a small abbreviation map (street/st, saint/st, mount/mt,
   doctor/dr, versus/vs, number/no): uploaders write "700 Main St" where the release says "Street",
-  which had rejected the correct official Art Track in every step. Unit-tested in
-  `backend/test/ytdlp.test.js`.
+  which had rejected the correct official Art Track in every step. One exception: a **re-release year
+  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`.
 - **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