Resume pending action after login (favorite, diary, QR upload)

Add pendingAction callback to UI store. When user clicks favorite,
save-to-diary, or upload QR while not logged in, the action is stored
and automatically executed after successful login/register instead of
reloading the page.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/LoginModal.vue

@@ -104,8 +104,11 @@ async function submit() {
       ui.showToast('注册成功')
     }
     emit('close')
-    // Reload page data after auth change
-    window.location.reload()
+    if (ui.pendingAction) {
+      ui.runPendingAction()
+    } else {
+      window.location.reload()
+    }
   } catch (e) {
     errorMsg.value = e?.message || (mode.value === 'login' ? '登录失败，请检查用户名和密码' : '注册失败，请重试')
   } finally {