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

client/src/api/featureFlags.ts

@@ -0,0 +1,47 @@
+import { apiRequestData } from "./http";
+
+export type FeatureFlagKey = "erp_sync" | "invoice_verification";
+export type FeatureFlagOverrideMode = "inherit" | "force_on" | "force_off";
+export type FeatureFlagRolloutType = "global" | "department_allowlist";
+
+export type FeatureFlagItem = {
+  id: string | null;
+  flagKey: FeatureFlagKey;
+  overrideMode: FeatureFlagOverrideMode;
+  rolloutType: FeatureFlagRolloutType;
+  departmentIds: string[];
+  note: string;
+  version: number;
+  createdAt: string | null;
+  createdBy: string | null;
+  updatedAt: string | null;
+  updatedBy: string | null;
+  envEnabled: boolean;
+  effectiveEnabled: boolean;
+  effectiveReason: string;
+  matchedDepartmentId: string | null;
+  requiresDepartment: boolean;
+};
+
+export type FeatureFlagListResponse = {
+  items: FeatureFlagItem[];
+};
+
+export type FeatureFlagUpdatePayload = {
+  overrideMode: FeatureFlagOverrideMode;
+  rolloutType: FeatureFlagRolloutType;
+  departmentIds: string[];
+  note: string;
+  expectedVersion: number;
+};
+
+export async function fetchFeatureFlags() {
+  return apiRequestData<FeatureFlagListResponse>("/api/system/feature-flags");
+}
+
+export async function updateFeatureFlag(flagKey: FeatureFlagKey, payload: FeatureFlagUpdatePayload) {
+  return apiRequestData<{ item: FeatureFlagItem }>(`/api/system/feature-flags/${flagKey}`, {
+    method: "PUT",
+    body: JSON.stringify(payload),
+  });
+}