feat(stats): shareable Top-Albums card export (#425)

* feat(stats): add shareable Top-Albums card export

Adds a shareable PNG export of the user's most-played albums,
available from the Statistics page under the "Most Played Albums"
section header.

Layout:
* 3 formats — Story (1080×1920, 9:16), Square (1080×1080), Twitter
  Card (1200×675, 16:9). Story and Square stack a centered URL footer;
  Twitter packs logo + label + URL into a single header row.
* 3 grid sizes — 3×3 (default), 4×4, 5×5. Modal fetches up to 25
  frequent albums on open so larger grids work even when the entry
  surface only loaded a handful.
* Cover tiles render the rank + play count in a thin black info strip
  at the bottom of the cover (rank left, "N Plays" right).
* Header label is hardcoded English ("Top Albums") so a shared image
  remains legible to followers who don't share the user's UI language.
  Caller can override via `opts.meta`.

Source path is local-only — `getAlbumList(type='frequent')` from
Subsonic. Last.fm is intentionally not used.

Implementation:
* `src/utils/exportAlbumCard.ts` — pure Canvas-API renderer. Reads
  theme accent / bg from the document's CSS variables so the export
  matches the active theme. Cover art is loaded through the existing
  `getCachedBlob` IndexedDB cache, so repeated exports are cheap.
  Wordmark is rendered from the `PsysonicLogo` React component via
  `renderToStaticMarkup`, with both gradient stops baked to a single
  accent color for crisp single-tone branding.
* `src/components/StatsExportModal.tsx` — UI: format + grid pickers,
  live downscaled preview, native save dialog via
  `@tauri-apps/plugin-dialog` + `plugin-fs`.
* `src/components/AlbumRow.tsx` — adds optional `headerExtra` slot so
  the share button sits next to the existing scroll-nav arrows.
* i18n keys added under `statistics.*` (`en`, `de`) — other locales
  fall back to English.

* docs(changelog): add Top-Albums card export for PR #425

src/components/AlbumRow.tsx

@@ -13,9 +13,11 @@ interface Props {
   moreText?: string;
   onLoadMore?: () => Promise<void>;
   showRating?: boolean;
+  /** Optional content rendered in the row header, left of the scroll-nav. */
+  headerExtra?: React.ReactNode;
 }
 
-export default function AlbumRow({ title, titleLink, albums, moreLink, moreText, onLoadMore, showRating }: Props) {
+export default function AlbumRow({ title, titleLink, albums, moreLink, moreText, onLoadMore, showRating, headerExtra }: Props) {
   const { t } = useTranslation();
   const scrollRef = useRef<HTMLDivElement>(null);
   const navigate = useNavigate();
@@ -71,15 +73,16 @@ export default function AlbumRow({ title, titleLink, albums, moreLink, moreText,
           <h2 className="section-title" style={{ marginBottom: 0 }}>{title}</h2>
         )}
         <div className="album-row-nav">
-          <button 
-            className={`nav-btn ${!showLeft ? 'disabled' : ''}`} 
+          {headerExtra}
+          <button
+            className={`nav-btn ${!showLeft ? 'disabled' : ''}`}
             onClick={() => scroll('left')}
             disabled={!showLeft}
           >
             <ChevronLeft size={20} />
           </button>
-          <button 
-            className={`nav-btn ${!showRight ? 'disabled' : ''}`} 
+          <button
+            className={`nav-btn ${!showRight ? 'disabled' : ''}`}
             onClick={() => scroll('right')}
             disabled={!showRight}
           >