docs(changelog): note duplicate check is case-sensitive (filename FS match)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -242,8 +242,9 @@ Versioning: two-part `MAJOR.MINOR` — each release bumps the minor (features an
   duplicate check matches the exact computed path only (same album folder, exact track-number
   prefix, exact resolved artist/title). Any drift between runs — different iTunes/romaji name, a
   different track number, a different album folder, or a `- Piano Version`/`(var)` variant suffix
-  — makes the file look new. Should match by normalized first-artist + title across the artist's
-  folders, not the exact path.
+  — makes the file look new. The check is also case-sensitive (filename-existence on a
+  case-sensitive Linux FS), so `DJ OKAWARI` vs `DJ Okawari` misses too. Should match by
+  normalized, case-insensitive first-artist + title across the artist's folders, not the exact path.
 - **Backend (download)** — The no-duration branch (tracks where iTunes returns no duration) has
   **no Mittelweg protection**: it still falls through to title-only / no-filter grabs and pulls
   wrong covers by other uploaders (observed: `Yorushika – 車窓` saved as `Piano Echoes – Shasou`).