fix(tz): server-side timezone conversion for all user-facing time displays

The audit showed only 5 of ~11 time-display surfaces converted to the
user's timezone; everything else rendered pgx-decoded UTC. The server
owns conversion — clients (web/app/KOReader) receive display-ready
strings or machine-readable instants and never convert.

- Progress page: LastUpdated formatted in the requesting user's tz
  (was raw UTC).
- Analytics: date-range defaults, day buckets, most-active-day, device
  last-sync, and popular-book last-read all computed in the user's tz —
  evening sessions no longer land on the next UTC day. Also fixed the
  end-date boundary: the query bounds with <= and the end bound was
  midnight, so the end date's own sessions (including 'today') never
  appeared.
- Queue page: new created_at_display field (admin tz) rendered by the
  template; created_at stays RFC3339 for API consumers.
- Admin hash-conflicts SSR bridge: detected date rendered in the
  admin's tz.
- OPDS: .UTC() before the Z-suffixed feed timestamps (honesty fix —
  correct today only because the session zone happens to be UTC).
- KOReader annotation datetimes deliberately untouched (device owns its
  display).

internal/router/frontend.go

@@ -1071,7 +1071,7 @@ func registerFrontendRoutes(cfg *Config) {
 				LibraryName: p.LibraryName,
 				SHA256:      p.FileSha256,
 				SHAShort:    p.FileSha256[:16] + "…",
-				CreatedAt:   p.CreatedAt.Time.Format("Jan 2, 2006"),
+				CreatedAt: p.CreatedAt.Time.In(utils.UserLocation(user.Timezone)).Format("Jan 2, 2006"),
 				Items:       []templates.HashConflictItemData{},
 			}