feat(albums): date-only pickers for start/end (create & edit, admin + app)

- 管理后台：DatePicker type=datetime → date；提交归一（开始=当天 00:00、
  结束=当天 23:59 整天活动语义；契约仍 datetime 仅交互粒度）
- App：去掉时间选择步骤（选日期即定；同上归一）；表单显示只显 yyyy/M/d
- e2e 日期填入改 '2026-10-01'（date 格式）；widget 断言日期粒度
- admin 87/87 + build、app 397/397 全绿

Co-Authored-By: Claude Code <noreply@anthropic.com>

apps/mobile/lib/pages/album_form_page.dart

@@ -355,17 +355,14 @@ class _AlbumFormPageState extends ConsumerState<AlbumFormPage>
       lastDate: DateTime(2100),
     );
     if (pickedDate == null || !mounted) return;
-    final pickedTime = await showTimePicker(
-      context: context,
-      initialTime: TimeOfDay(hour: wall.hour, minute: wall.minute),
-    );
-    if (pickedTime == null || !mounted) return;
+    // UI06（用户需求 2026-09-23）：只选日期不带时间——开始=当天 00:00，
+    // 结束=当天 23:59（活动整天语义；契约仍为 datetime，仅交互粒度变化）。
     final naive = DateTime(
       pickedDate.year,
       pickedDate.month,
       pickedDate.day,
-      pickedTime.hour,
-      pickedTime.minute,
+      isStart ? 0 : 23,
+      isStart ? 0 : 59,
     );
     final utc = albumWallClockToUtc(naive, tzName);
     setState(() {
@@ -764,9 +761,13 @@ class _AlbumFormPageState extends ConsumerState<AlbumFormPage>
     final l10n = AppLocalizations.of(context);
     final theme = Theme.of(context);
     final value = isStart ? _startAt : _endAt;
-    final formatted = value == null
+    // 只显日期（选择粒度为日期；时间由开始/结束日的 00:00/23:59 语义承载）。
+    final wallShown = value == null
         ? null
-        : formatAlbumDateTime(value, _timezone.text, l10n.localeName);
+        : (tryToAlbumZone(value, _timezone.text.trim()) ?? value.toUtc());
+    final formatted = wallShown == null
+        ? null
+        : '${wallShown.year}/${wallShown.month}/${wallShown.day}';
     return Padding(
       padding: const EdgeInsets.only(bottom: 12),
       child: InkWell(