docs(changelog): Dublettenprüfung nachgezogen, Unterstrich-Lücke im Variantenfilter notiert

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

CHANGELOG.md

@@ -745,6 +745,12 @@ Polish release: Android navigation and offline resilience, download accuracy for
 ### Known Bugs
 - **Android (lyrics)** — Synced-lyrics auto-scroll is **not smooth**: it follows playback and highlights the right line, but the list jumps to it rather than gliding. Web autoscroll is smooth. Not yet fixed.
 - **Web (PWA, desktop)** — The Windows media tile (SMTC) briefly closes and reopens when skipping tracks. Swapping the `<audio>` element's source leaves a momentary gap with no active media output, so Windows tears down and rebuilds the tile. A real fix needs one continuous source (MSE), which requires streaming an MSE-compatible format. The native Android app is unaffected. (The two-element gapless handoff added in 1.1 makes skips effectively instant but does **not** fix this — switching elements still ends and restarts the OS session.)
-- **Backend (download)** — The duplicate check requires at least a `firstArtist` folder match. If the same song was previously stored under a very different artist name (e.g. before an iTunes-name fix), it will not be detected as a duplicate and will be re-downloaded.
+- **Backend (download)** — Die Dublettenprüfung sucht in den Ordnern von Album- **und** Titel-Künstler
+  und ignoriert Akzente sowie Apostrophe (2.3). Ein Rest bleibt: steht derselbe Song unter einem
+  **deutlich anderen** Künstlernamen (etwa vor einer Namenskorrektur), wird er weiterhin nicht
+  erkannt und erneut geladen.
+- **Backend (download)** — Der Variantenfilter nutzt `\b`-Wortgrenzen, und die zählen den Unterstrich
+  als Wortzeichen. Titel wie `song_instrumental_cover` oder `Easy_live` rutschen deshalb durch,
+  während `Easy (Instrumental)` korrekt abgewiesen wird.
 - **Backend (metadata/sorting)** — MusicBrainz `release['artist-credit']` is often absent in the standard recording search response (requires `inc=artist-credits` which can slow the endpoint). The albumArtist field from MusicBrainz autofill may fall back to the recording artist rather than the release artist.
 - **Backend (metadata/sorting)** — MBIDs are not embedded in downloaded tracks; Navidrome cannot use them for authoritative album grouping (low priority — album splitting is mostly solved via consistent `album_artist`).