feat(detail): mark read chapters and count new ones on the manga page

On the manga detail page, dim chapters at or before the reader's last-read
chapter (with an accent check + screen-reader "Read." label) and show a
"N new since last read" badge counting chapters that have landed since.
All client-side from the already-loaded chapter list and per-manga read
progress — no extra requests. The count reflects the loaded (paginated)
chapter list. Logic lives in a pure, unit-tested chapterProgress helper;
e2e covers the mid-series and never-opened cases.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.96.0",
+  "version": "0.97.0",
   "private": true,
   "type": "module",
   "scripts": {