fix(statistics): cache Subsonic stat fetches and localize duration units

Add 7-minute TTL caches (same idea as rating prefetch) for overview
album strips, random-song format sample, and paginated library
aggregates; key by server and music folder.

Introduce formatHumanHoursMinutes with common.duration* strings in all
locales for Statistics and playlist duration labels.

Refresh RU/ZH statistics and nav wording; fix zh playtime label.

src/locales/en.ts

@@ -362,6 +362,8 @@ export const enTranslation = {
     updaterAurHint: 'Install the update via AUR:',
     updaterErrorMsg: 'Download failed',
     updaterRetryBtn: 'Retry',
+    durationHoursMinutes: '{{hours}}h {{minutes}}m',
+    durationMinutesOnly: '{{minutes}}m',
     updaterOpenGitHub: 'Open on GitHub',
   },
   settings: {