feat(P11-P12): 落地治理开关与移动端MVP（G0-G6/H1/M1-M4）

- 新增 Feature Flag 模型、评估服务与管理 API（erp_sync/invoice_verification）\n- 完成 ERP 与验真灰度收口（路由/服务/作业统一判定）\n- 补齐 pay 与手动 sync 的 department_id 灰度上下文\n- 增加管理后台开关页、PWA 基础设施与移动拍照/审批页面\n- 增加回归脚本、安全基线与压测脚本，更新文档与执行合同\n\nIssue: G0,G1,G2,G3,G4,G5,G6,H1,M1,M2,M3,M4

server/src/app.js

@@ -28,6 +28,7 @@ const employeesRoutes = require("./routes/employees");
 const expenseTypesRoutes = require("./routes/expenseTypes");
 const configReadRoutes = require("./routes/configRead");
 const approvalRulesRoutes = require("./routes/approvalRules");
+const featureFlagsRoutes = require("./routes/featureFlags");
 const notificationsRoutes = require("./routes/notifications");
 const exportsRoutes = require("./routes/exports");
 const dashboardRoutes = require("./routes/dashboard");
@@ -229,6 +230,7 @@ async function buildApp() {
   await app.register(expenseTypesRoutes, { prefix: "/api" });
   await app.register(configReadRoutes, { prefix: "/api" });
   await app.register(approvalRulesRoutes, { prefix: "/api" });
+  await app.register(featureFlagsRoutes, { prefix: "/api" });
   await app.register(notificationsRoutes, { prefix: "/api" });
   await app.register(dashboardRoutes, { prefix: "/api" });
   await app.register(budgetsRoutes, { prefix: "/api" });