feat(ui): use timezone-aware time formatting across all templates

Replace hardcoded .Format() calls with FormatInTimezone() and
FormatTimestamptzInTimezone() helpers so all timestamps display in
the user's selected timezone.

Changes:
- book_detail.templ: remove incorrect templates. package prefix
- book_detail_modals.templ: add User param to ProgressSyncModal so
  timezone is available; convert Timestamp to FormatInTimezone()
- devices.templ: convert LastSync and LastSeen to FormatInTimezone()
- conflicts.templ: convert CreatedAt to FormatInTimezone()
- admin_users.templ: convert CreatedAt to FormatInTimezone() using
  currentUser.Timezone

Note: DatePublished is kept as a plain date format (MM-DD-YYYY) since
it is a pgtype.Date, not a timestamp, and does not need timezone
conversion.

templates/admin_users.templ

@@ -86,7 +86,7 @@ templ AdminUsers(currentUser User, users []User, adminCount int) {
 										</td>
 										<!-- Created -->
 										<td class="px-6 py-4 whitespace-nowrap">
-											<div class="text-sm" style="color: var(--text-secondary)">{ user.CreatedAt.Format("01-02-2006") }</div>
+											<div class="text-sm" style="color: var(--text-secondary)">{ FormatInTimezone(user.CreatedAt, currentUser.Timezone) }</div>
 										</td>
 										<!-- Actions -->
 										<td class="px-6 py-4 whitespace-nowrap text-right">