feat: enhance DND nesting & promotion, isolated tags API, fix completion bounce UI, add Admin i18n switcher, refine typography & polish UX (v0.7.2)

src/components/layout/AppShell.tsx

@@ -5,6 +5,7 @@ import { TaskList, Task, List, User } from "../tasks/TaskList";
 import { useUserPrefs, usePrefsStyle } from "@/lib/useUserPrefs";
 import { TaskDetail } from "../tasks/TaskDetail";
 import { CommandPalette } from "../ui/CommandPalette";
+import { useI18n } from "@/lib/i18n";
 import {
   getDemoStore,
   saveDemoStore,
@@ -58,6 +59,7 @@ export function AppShell({ user, isDemo = false }: AppShellProps) {
   const [showCompleted, setShowCompleted] = useState(false);
   const [cmdPaletteOpen, setCmdPaletteOpen] = useState(false);
   const [refreshKey, setRefreshKey] = useState(0);
+  const { t } = useI18n();
 
   // Global user preferences (reactive)
   const { prefs, updatePrefs } = useUserPrefs();
@@ -677,12 +679,12 @@ export function AppShell({ user, isDemo = false }: AppShellProps) {
           <div className="undo-toast-content">
             <span className="undo-toast-icon">🗑️</span>
             <span className="undo-toast-msg">
-              <strong>{undoToast.title || "할 일"}</strong>이(가) 삭제되었습니다.
+              <strong>{undoToast.title || t("tasks")}</strong> {t("taskUndoHint")}
             </span>
           </div>
           <div className="undo-toast-actions">
             <button type="button" className="undo-toast-btn" onClick={handleUndoDelete}>
-              실행 취소
+              {t("undoDelete")}
             </button>
             <button
               type="button"