feat(frontend): Phase C 固定企业模式 - VITE_FIXED_ENTITY_ID 支持登录无下拉/隐藏切换器

- 新增 src/utils/entity.ts: isFixedEntity/getFixedEntityId/effectiveEntityId
- Login.vue: 固定企业版隐藏企业下拉显示只读徽标, 登录直接带固定 entity_id
- MainLayout.vue: 切换器加 !isFixedEntity() 守卫, 固定版顶部显示企业 tag, logo 带企业名
- ReportCenter.vue: 页内企业切换下拉加守卫, getEntityId 固定版恒取构建锁定值
- .env.example: VITE_FIXED_ENTITY_ID 示例与说明
- 验证脚本 backend/scripts/verify_phase_c_fixed_entity_e2e.py (22项, 双build E2E全过)

frontend/src/views/ReportCenter.vue

@@ -4,7 +4,10 @@
     <div class="report-header">
       <h3 class="page-title">📊 CMA管理报表</h3>
       <div class="header-right">
+        <!-- 固定企业版（Phase C）：页内切换下拉隐藏，显示当前企业 tag -->
+        <el-tag v-if="isFixedEntity()" size="small" type="primary" effect="plain">{{ currentEntityNameTag }}</el-tag>
         <el-select
+          v-else
           v-model="currentEntityId"
           size="small"
           style="width:180px"
@@ -624,9 +627,10 @@
 </template>
 
 <script setup lang="ts">
-import { ref, reactive, onMounted, nextTick } from 'vue'
+import { ref, reactive, computed, onMounted, nextTick } from 'vue'
 import { ElMessage } from 'element-plus'
 import axios from 'axios'
+import { isFixedEntity, getFixedEntityId } from '../utils/entity'
 
 // ── 状态 ──
 const loading = ref(false)
@@ -637,7 +641,17 @@ const reportPeriod = ref('2026-06')
 const entities = ref<any[]>([])
 const currentEntityId = ref(Number(localStorage.getItem('cma_entity_id') || 1))
 
+// 固定企业版：页内切换下拉隐藏，右上角显示当前企业 tag
+const currentEntityNameTag = computed(() => {
+  const f = getFixedEntityId()
+  const n = localStorage.getItem('cma_entity_name')
+  return n || (f !== undefined ? `企业 #${f}` : '')
+})
+
 function getEntityId() {
+  // 固定企业版恒取构建锁定值（防 localStorage 残留串账套）；切换版取登录/切换写入值
+  const f = getFixedEntityId()
+  if (f !== undefined) return f
   return Number(localStorage.getItem('cma_entity_id') || currentEntityId.value || 1)
 }
 
@@ -667,9 +681,10 @@ async function onEntityChange(id: number) {
   }
 }
 
-// 跨页面同步：其他页面切换企业时联动刷新
+// 跨页面同步：其他页面切换企业时联动刷新（固定企业版忽略——该版本不存在切换）
 if (typeof window !== 'undefined') {
   window.addEventListener('storage', (ev: StorageEvent) => {
+    if (isFixedEntity()) return
     if (ev.key === 'cma_entity_id' && ev.newValue) {
       currentEntityId.value = Number(ev.newValue)
       loadAll()
@@ -1063,7 +1078,7 @@ function onBudgetSort(sort: any) {
 }
 
 onMounted(() => {
-  loadEntities()
+  if (!isFixedEntity()) loadEntities()
   loadKpiOptions()
   loadAll()
   loadStatutory()