feat(app-shell): 桌面端集成自动更新（electron-updater）

- 集成 electron-updater：检查更新/下载/安装/忽略此版本，并推送下载进度到前端

- 打包版启动后自动检查更新；托盘菜单支持手动检查

- preload 暴露 updater IPC + __brand 标记；前端新增更新弹窗与设置页版本/检查更新入口

- 补全发布配置：artifactName/publish；release workflow 增加上传 latest.yml

frontend/components/DesktopUpdateDialog.vue

@@ -0,0 +1,164 @@
+<template>
+  <Teleport to="body">
+    <div v-if="open && info" class="fixed inset-0 z-[9999] flex items-center justify-center">
+      <div class="absolute inset-0 bg-black/40" @click="onBackdropClick" />
+
+      <div class="relative w-[min(520px,calc(100vw-32px))] rounded-lg bg-white shadow-xl border border-gray-200">
+        <button
+          class="absolute right-3 top-3 h-8 w-8 rounded-md text-gray-500 hover:bg-gray-100 hover:text-gray-700"
+          type="button"
+          @click="emitClose"
+          aria-label="Close"
+        >
+          <span class="text-xl leading-none">&times;</span>
+        </button>
+
+        <div class="px-5 pt-5 pb-4">
+          <div class="text-xs text-gray-500">
+            {{ readyToInstall ? '更新已下载完成' : '发现新版本' }}
+          </div>
+          <div class="mt-1 text-lg font-semibold text-gray-900">
+            {{ info.version || '—' }}
+          </div>
+
+          <div v-if="readyToInstall" class="mt-2 text-xs text-gray-600">
+            你可以选择现在重启安装，或稍后再安装。
+          </div>
+
+          <div class="mt-4 rounded-md border border-gray-200 bg-gray-50 p-3">
+            <div class="text-xs font-medium text-gray-700">更新内容</div>
+            <div class="mt-2 text-xs text-gray-700 whitespace-pre-wrap break-words">
+              {{ info.releaseNotes || '修复了一些已知问题，提升了稳定性。' }}
+            </div>
+          </div>
+
+          <div v-if="error" class="mt-3 text-xs text-red-600 whitespace-pre-wrap break-words">
+            {{ error }}
+          </div>
+
+          <div v-if="isDownloading" class="mt-4">
+            <div class="flex items-center justify-between gap-3 text-xs text-gray-600">
+              <span v-if="speedText">{{ speedText }}</span>
+              <span v-else>下载中...</span>
+              <span>{{ percentText }}</span>
+              <span v-if="remainingText">剩余 {{ remainingText }}</span>
+            </div>
+            <div class="mt-2 h-2 w-full rounded bg-gray-200 overflow-hidden">
+              <div class="h-2 bg-emerald-500" :style="{ width: `${percent}%` }" />
+            </div>
+          </div>
+
+          <div v-if="isDownloading" class="mt-5 flex items-center justify-end gap-2">
+            <button
+              class="px-3 py-1.5 rounded-md border border-gray-200 bg-white text-sm text-gray-700 hover:bg-gray-50"
+              type="button"
+              @click="emitClose"
+            >
+              后台下载
+            </button>
+          </div>
+
+          <div v-else class="mt-5 flex items-center justify-end gap-2">
+            <button
+              class="px-3 py-1.5 rounded-md border border-gray-200 bg-white text-sm text-gray-700 hover:bg-gray-50"
+              type="button"
+              @click="emitClose"
+            >
+              稍后
+            </button>
+
+            <button
+              v-if="readyToInstall"
+              class="px-3 py-1.5 rounded-md bg-emerald-600 text-white text-sm hover:bg-emerald-700"
+              type="button"
+              @click="emitInstall"
+            >
+              立即重启安装
+            </button>
+
+            <template v-else>
+              <button
+                v-if="hasIgnore"
+                class="px-3 py-1.5 rounded-md border border-gray-200 bg-white text-sm text-gray-700 hover:bg-gray-50"
+                type="button"
+                @click="emitIgnore"
+              >
+                忽略此版本
+              </button>
+              <button
+                class="px-3 py-1.5 rounded-md bg-emerald-600 text-white text-sm hover:bg-emerald-700"
+                type="button"
+                @click="emitUpdate"
+              >
+                立即更新
+              </button>
+            </template>
+          </div>
+        </div>
+      </div>
+    </div>
+  </Teleport>
+</template>
+
+<script setup>
+const props = defineProps({
+  open: { type: Boolean, default: false },
+  info: { type: Object, default: null }, // { version, releaseNotes }
+  isDownloading: { type: Boolean, default: false },
+  readyToInstall: { type: Boolean, default: false },
+  progress: { type: [Number, Object], default: () => ({ percent: 0 }) },
+  error: { type: String, default: "" },
+  hasIgnore: { type: Boolean, default: true },
+});
+
+const emit = defineEmits(["close", "update", "install", "ignore"]);
+
+const safeProgress = computed(() => {
+  if (typeof props.progress === "number") return { percent: props.progress };
+  if (props.progress && typeof props.progress === "object") return props.progress;
+  return { percent: 0 };
+});
+
+const percent = computed(() => {
+  const p = Number(safeProgress.value?.percent || 0);
+  if (!Number.isFinite(p)) return 0;
+  return Math.max(0, Math.min(100, p));
+});
+
+const percentText = computed(() => `${percent.value.toFixed(0)}%`);
+
+const formatBytes = (bytes) => {
+  const b = Number(bytes || 0);
+  if (!Number.isFinite(b) || b <= 0) return "0 B";
+  const k = 1024;
+  const sizes = ["B", "KB", "MB", "GB", "TB"];
+  const i = Math.floor(Math.log(b) / Math.log(k));
+  const idx = Math.max(0, Math.min(i, sizes.length - 1));
+  return `${(b / Math.pow(k, idx)).toFixed(1)} ${sizes[idx]}`;
+};
+
+const speedText = computed(() => {
+  const bps = safeProgress.value?.bytesPerSecond;
+  if (bps == null) return "";
+  return `${formatBytes(bps)}/s`;
+});
+
+const remainingText = computed(() => {
+  const s = safeProgress.value?.remaining;
+  const sec = Number(s);
+  if (!Number.isFinite(sec)) return "";
+  if (sec < 60) return `${Math.ceil(sec)} 秒`;
+  const min = Math.floor(sec / 60);
+  const rem = Math.ceil(sec % 60);
+  return `${min} 分 ${rem} 秒`;
+});
+
+const emitClose = () => emit("close");
+const emitUpdate = () => emit("update");
+const emitInstall = () => emit("install");
+const emitIgnore = () => emit("ignore");
+
+const onBackdropClick = () => {
+  emitClose();
+};
+</script>