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/public/manifest.webmanifest

@@ -0,0 +1,27 @@
+{
+  "name": "hyb-oa 移动工作台",
+  "short_name": "hyb-oa",
+  "description": "海音达工作台移动端入口，支持离线拍照上传与移动审批。",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#ffffff",
+  "theme_color": "#2563eb",
+  "icons": [
+    {
+      "src": "/pwa-192x192.png",
+      "sizes": "192x192",
+      "type": "image/png"
+    },
+    {
+      "src": "/pwa-512x512.png",
+      "sizes": "512x512",
+      "type": "image/png"
+    },
+    {
+      "src": "/pwa-maskable-512x512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
+    }
+  ]
+}