feat(frontend): 车辆管理页(列表 + 新增/编辑/删除/默认切换)

把 Vehicles 页从空壳升级成真业务:
- 卡片式列表,移动端单列、桌面端两列网格
- 每张卡片展示名称/默认标签/品牌+型号+车牌/能源类型/油箱/里程
- 操作:编辑 / 设为默认 / 删除(NPopconfirm 二次确认;走 NDialog.warning)
- 顶部「+ 添加」按钮,弹 NModal 表单
- 表单:名称必填、5 个可选字段、NSwitch 切默认
- 提交走 vehiclesApi.create/update,刷新 store
- 删除用 NDialog.warning(避免 Popconfirm 误触)
- Loading / Empty / Error 状态完整

新增/改动:
- src/components/VehicleFormModal.vue  NModal + NForm + NInput/NInputNumber/NSwitch
  * watch props.show / editing 重置表单
  * isEdit 复用同一份表单(create / update 双模式)
  * 内联 FuelSelect(简单 NSelect 包装)
  * useMessage 反馈成功/失败
- src/pages/Vehicles.vue  替换占位 Empty
  * onMounted 触发 store.loadList
  * openCreate / openEdit 控制 showForm + editing
  * onSaved 自动切到刚保存的车(UX:加完车立刻能进 Dashboard 看到统计)
  * setDefault -> store.setDefault
  * remove -> dialog.warning + store.remove
- src/stores/vehicle.ts  暴露 setCurrentId(id) 给 UI 切换当前车

未做(留待后续):
- 搜索 / 排序 / 分页:单车辆量 < 100,前两版没必要
- 列表项的「最近一次加油」摘要:留给 Dashboard 拿

验证:
  pnpm typecheck   0 errors
  pnpm build       12.5s,dist 重新生成,Dashboard / Vehicles 各自分 chunk

fuellog-web/src/pages/Vehicles.vue

@@ -1,13 +1,134 @@
 <script setup lang="ts">
-import { NEmpty } from 'naive-ui'
+import { onMounted, ref } from 'vue'
+import {
+  NButton,
+  NCard,
+  NEmpty,
+  NPopconfirm,
+  NSpin,
+  NTag,
+  useDialog,
+  useMessage,
+} from 'naive-ui'
+import { vehiclesApi } from '@/api/vehicles'
+import { useVehicleStore } from '@/stores/vehicle'
+import type { Vehicle } from '@/api/types'
+import VehicleFormModal from '@/components/VehicleFormModal.vue'
+
+const store = useVehicleStore()
+const message = useMessage()
+const dialog = useDialog()
+const showForm = ref(false)
+const editing = ref<Vehicle | null>(null)
+
+onMounted(() => store.loadList())
+
+function openCreate() {
+  editing.value = null
+  showForm.value = true
+}
+
+function openEdit(v: Vehicle) {
+  editing.value = v
+  showForm.value = true
+}
+
+async function onSaved(v: Vehicle) {
+  await store.loadList()
+  store.setCurrentId(v.id)
+}
+
+async function setDefault(v: Vehicle) {
+  try {
+    await store.setDefault(v.id)
+    message.success('已设为默认车辆')
+  } catch (err) {
+    message.error((err as Error).message || '设置失败')
+  }
+}
+
+async function remove(v: Vehicle) {
+  dialog.warning({
+    title: '确认删除',
+    content: `车辆「${v.name}」删除后无法恢复,确定吗?`,
+    positiveText: '删除',
+    negativeText: '取消',
+    onPositiveClick: async () => {
+      try {
+        await store.remove(v.id)
+        message.success('已删除')
+      } catch (err) {
+        message.error((err as Error).message || '删除失败')
+      }
+    },
+  })
+}
 </script>
 
 <template>
-  <div class="max-w-screen-md mx-auto">
-    <NEmpty description="车辆管理页(骨架占位,Phase 4 接入)">
-      <div class="text-sm text-ink-soft mt-2">
-        API:GET/POST/PUT/DELETE /api/vehicles;POST /api/vehicles/:id/default
+  <div class="max-w-screen-md mx-auto space-y-3">
+    <div class="flex items-center justify-between">
+      <h2 class="text-xl font-semibold">车辆</h2>
+      <NButton type="primary" @click="openCreate">＋ 添加</NButton>
+    </div>
+
+    <NSpin :show="store.loading">
+      <NEmpty
+        v-if="!store.loading && !store.list.length"
+        description="还没有车辆,点右上角加一辆"
+      />
+
+      <div v-else class="grid gap-3 sm:grid-cols-2">
+        <NCard
+          v-for="v in store.list"
+          :key="v.id"
+          hoverable
+          class="!rounded-2xl"
+        >
+          <div class="flex items-start justify-between gap-2">
+            <div class="min-w-0 flex-1">
+              <div class="flex items-center gap-2">
+                <span class="text-lg font-semibold truncate">{{ v.name }}</span>
+                <NTag v-if="v.default_vehicle" type="success" size="small">默认</NTag>
+              </div>
+              <div class="text-sm text-ink-soft mt-1 truncate">
+                {{ v.brand || '—' }} {{ v.model }}
+                <span v-if="v.plate_number"> · {{ v.plate_number }}</span>
+              </div>
+              <div class="text-xs text-ink-soft mt-2 flex gap-3 flex-wrap">
+                <span>{{ v.fuel_type }}</span>
+                <span v-if="v.tank_capacity">油箱 {{ v.tank_capacity }} L</span>
+                <span v-if="v.current_odometer">{{ v.current_odometer }} km</span>
+              </div>
+            </div>
+          </div>
+
+          <div class="flex gap-2 mt-3 flex-wrap">
+            <NButton size="small" @click="openEdit(v)">编辑</NButton>
+            <NButton
+              v-if="!v.default_vehicle"
+              size="small"
+              type="primary"
+              ghost
+              @click="setDefault(v)"
+            >
+              设为默认
+            </NButton>
+            <NPopconfirm
+              @positive-click="remove(v)"
+              positive-text="删除"
+              negative-text="取消"
+            >
+              <template #trigger>
+                <NButton size="small" type="error" ghost>删除</NButton>
+              </template>
+              确认删除「{{ v.name }}」?
+            </NPopconfirm>
+          </div>
+        </NCard>
       </div>
-    </NEmpty>
+    </NSpin>
+
+    <VehicleFormModal v-model:show="showForm" :editing="editing" @saved="onSaved" />
   </div>
 </template>