feat(reader): chapter select dropdown for direct chapter jumps (0.51.0)

Adds a chapter `<select>` to the reader's top nav listing every chapter
of the current manga, defaulting to the open chapter; picking another
entry navigates straight to it without going back to the manga detail
page. Options use the "Ch. N — Title" form to match the existing
chapter tile and prev/next buttons in the reader bar.

Covered by a new Playwright spec.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.50.0",
+  "version": "0.51.0",
   "private": true,
   "type": "module",
   "scripts": {