fix(audio player + dashboard): markdown bookmark notes, horizontal volume, transport glyphs, client-side badges

Bookmarks: notes are markdown now — capture and drawer edit are
textareas (raw source), display renders through the reader's
markdown-it + DOMPurify pipeline (renderNoteHtml) as x-html; the
edit textarea drops the enter-to-save handler so newlines survive.

Volume: the panel dragger is horizontal (mute button beside it,
7.5rem slider) per user feedback — vertical orientation read as a
scrubber clone at a glance.

Play/pause: unicode glyphs replaced with SVG — the triangle is
optically centered (2px right-bias) and the pause bars are longer
and thicker rounded rects (4.2×15 at rx 1.7).

Dashboard: the client-side card renderer (dashboard.ts — the path the
JSON sections actually render through) now mirrors the templ BookCard:
cover-corner badges for audiobook/comic/manga (books unbadged) and the
hover action shows headphones with 'Listen to …' labels for audiobooks.
BookInfo type + Go struct carry format_group end to end.

Verified on-device: pause glyph centered/thicker, horizontal volume
panel, markdown note ('**bold**' + list) rendered in the bookmarks
drawer, badges on dashboard cards, sections JSON carrying
format_group.

web/src/types/api.d.ts

@@ -102,6 +102,7 @@ interface BookInfo {
   author: string;
   cover_image_path: string;
   has_conflict: boolean;
+  format_group: string;
 }
 
 // Dashboard type definitions