feat(themes): Theme Store install counts, downloads & sort (#1036)

* feat(themes): install counts, downloads, popularity & sort in the Theme Store

Each registry theme now carries an install count and a last-changed date. Store
rows show them in a dedicated meta panel (author, popularity bar, total
downloads, last changed), plus a sort dropdown (most popular / newest / name),
zebra-striped rows, a numbered pager, and a note that the stats refresh daily.
Adds a shared formatRelativeTime helper (formatLastSeen now delegates to it).

* test(themes): cover sort modes, pager jump and relative-time formatting

* fix(build): gate nvidia_quirk_active to Linux

Its only caller is the Linux branch of theme_animation_risk, so on Windows and
macOS the function was dead code and tripped clippy's -D warnings.

* docs: CHANGELOG + credits for theme store download stats & sort (#1036)

src/locales/de/settings.ts

@@ -329,6 +329,7 @@ export const settings = {
   themeStoreSubmitText: 'Eigenes Theme gebaut? Teil es mit der Community — mehr Infos im Themes-Repository.',
   themeStoreSubmitLink: 'Themes-Repository öffnen',
   themeStoreNetworkNotice: 'Der Theme-Store lädt Katalog und Vorschauen von externen Diensten (jsDelivr-CDN und GitHub). Es werden keine persönlichen Daten gesendet.',
+  themeStoreStatsNotice: 'Download- und „Zuletzt geändert"-Statistiken werden einmal täglich aktualisiert (gegen 04:17 UTC).',
   themeStoreSearchPlaceholder: 'Themes suchen…',
   themeStoreFilterMode: 'Nach Modus filtern',
   themeStoreModeAll: 'Alle',
@@ -342,7 +343,13 @@ export const settings = {
   themeStoreEmpty: 'Keine Themes passen zu deinen Filtern.',
   themeStoreActive: 'Aktiv',
   themeStoreEnlarge: 'Vorschau vergrößern',
-  themeStoreByAuthor: 'von {{author}}',
+  themeStoreSortPopular: 'Beliebteste',
+  themeStoreSortNewest: 'Neueste',
+  themeStoreSortName: 'Alphabetisch',
+  themeStoreAuthor: 'Autor',
+  themeStorePopularity: 'Beliebtheit',
+  themeStoreDownloads: 'Downloads gesamt',
+  themeStoreLastChanged: 'Zuletzt geändert',
   themeMigrationNoticeTitle: 'Theme in den Store gezogen',
   themeMigrationNoticeBody: '{{themes}} ist nicht mehr in der App enthalten. Du kannst es im Theme-Store neu installieren (Einstellungen → Themes) oder ein anderes Theme wählen.',
   themeMigrationNoticeOpen: 'Theme-Store öffnen',