feat(locale): 实现 App 启动时语言和时区自动设置

- 新增系统语言/时区读取工具函数
- SessionStore 扩展支持时区存储
- 启动流程自动检测并保存系统语言/时区
- 注册时传递语言/时区到后端
- 登录后从服务器同步语言/时区

apps/lib/shared/utils/time_format.dart

@@ -0,0 +1,30 @@
+import 'package:flutter/widgets.dart';
+
+import '../../l10n/app_localizations.dart';
+
+String formatRelativeTime(BuildContext context, DateTime dateTime) {
+  final l10n = AppLocalizations.of(context)!;
+  final diff = DateTime.now().difference(dateTime);
+  if (diff.inMinutes < 1) return l10n.timeJustNow;
+  if (diff.inHours < 1) return l10n.timeMinutesAgo(diff.inMinutes);
+  if (diff.inDays < 1) return l10n.timeHoursAgo(diff.inHours);
+  if (diff.inDays < 30) return l10n.timeDaysAgo(diff.inDays);
+  return '${dateTime.month}/${dateTime.day}';
+}
+
+String formatCompactLocalDateTime(String isoString) {
+  final dateTime = DateTime.parse(isoString).toLocal();
+  final now = DateTime.now();
+  final timeText =
+      '${dateTime.hour.toString().padLeft(2, '0')}:${dateTime.minute.toString().padLeft(2, '0')}';
+
+  if (now.year == dateTime.year &&
+      now.month == dateTime.month &&
+      now.day == dateTime.day) {
+    return timeText;
+  }
+
+  final dateText =
+      '${dateTime.year}-${dateTime.month.toString().padLeft(2, '0')}-${dateTime.day.toString().padLeft(2, '0')}';
+  return '$dateText $timeText';
+}