fix(web): update time locale when language is changed

Pass i18n.language to time display components to ensure locale updates
when the user switches languages in UserMenu. Changes:

- MemoView: Pass i18n.language to toLocaleString() and <relative-time> lang attribute
- MonthNavigator: Wrap with observer to make component reactive to i18n.language changes

🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>

web/src/components/MemoView.tsx

@@ -7,6 +7,7 @@ import { Tooltip, TooltipContent, TooltipProvider, TooltipTrigger } from "@/comp
 import useAsyncEffect from "@/hooks/useAsyncEffect";
 import useCurrentUser from "@/hooks/useCurrentUser";
 import useNavigateTo from "@/hooks/useNavigateTo";
+import i18n from "@/i18n";
 import { cn } from "@/lib/utils";
 import { instanceStore, memoStore, userStore } from "@/store";
 import { State } from "@/types/proto/api/v1/common";
@@ -211,9 +212,9 @@ const MemoView: React.FC<Props> = observer((props: Props) => {
   };
 
   const displayTime = isArchived ? (
-    memo.displayTime?.toLocaleString()
+    memo.displayTime?.toLocaleString(i18n.language)
   ) : (
-    <relative-time datetime={memo.displayTime?.toISOString()} format={relativeTimeFormat}></relative-time>
+    <relative-time datetime={memo.displayTime?.toISOString()} lang={i18n.language} format={relativeTimeFormat}></relative-time>
   );
 
   return showEditor ? (

web/src/components/StatisticsView/MonthNavigator.tsx

 import dayjs from "dayjs";
 import { ChevronLeftIcon, ChevronRightIcon } from "lucide-react";
+import { observer } from "mobx-react-lite";
 import i18n from "@/i18n";
 import type { MonthNavigatorProps } from "@/types/statistics";
 
-export const MonthNavigator = ({ visibleMonth, onMonthChange }: MonthNavigatorProps) => {
+export const MonthNavigator = observer(({ visibleMonth, onMonthChange }: MonthNavigatorProps) => {
   const currentMonth = dayjs(visibleMonth).toDate();
 
   const handlePrevMonth = () => {
@@ -29,4 +30,4 @@ export const MonthNavigator = ({ visibleMonth, onMonthChange }: MonthNavigatorPr
       </div>
     </div>
   );
-};
+});