docs(admin-portal): 新增 nextstep-v2.md 记录下游核查结果

v1 声称完成的下游工作经核查实际未完成：
- api-gateway: /api/admin/graphql 路由未注册，go vet 编译失败
- teacher-bff: resolver 已完成但 schema 未同步（命名空间 vs 扁平）
- iam: proto 缺 BatchGetUsers rpc 声明

v2 记录详细核查证据和修复要求

apps/teacher-portal/size-limit.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://raw.githubusercontent.com/ai/size-limit/main/schema.json",
   "name": "teacher-portal bundle size limits",
-  "description": "P6 性能预算：Shell <150KB / Remote <80KB / CSS <50KB",
+  "description": "P6 性能预算：Shell <150KB / Remote <80KB / CSS <50KB；路由 First Load JS 限额",
   "checks": [
     {
       "name": "Shell (main bundle)",
@@ -20,6 +20,51 @@
       "path": ".next/static/css/*.css",
       "limit": "50 KB",
       "gzip": true
+    },
+    {
+      "name": "Route / (首页)",
+      "path": [
+        ".next/static/chunks/app/(app)/page-*.js",
+        ".next/static/chunks/app/page-*.js"
+      ],
+      "limit": "90 KB",
+      "gzip": true
+    },
+    {
+      "name": "Route /grades/analytics (成绩分析)",
+      "path": ".next/static/chunks/app/(app)/grades/analytics/**/*.js",
+      "limit": "130 KB",
+      "gzip": true
+    },
+    {
+      "name": "Route /knowledge-graph (知识图谱)",
+      "path": ".next/static/chunks/app/(app)/knowledge-graph/**/*.js",
+      "limit": "120 KB",
+      "gzip": true
+    },
+    {
+      "name": "Route /questions (题目管理)",
+      "path": ".next/static/chunks/app/(app)/questions/**/*.js",
+      "limit": "130 KB",
+      "gzip": true
+    },
+    {
+      "name": "Route /lesson-plans/heatmap (热力图)",
+      "path": ".next/static/chunks/app/(app)/lesson-plans/heatmap/**/*.js",
+      "limit": "130 KB",
+      "gzip": true
+    },
+    {
+      "name": "Route /grades (成绩查询)",
+      "path": ".next/static/chunks/app/(app)/grades/page-*.js",
+      "limit": "130 KB",
+      "gzip": true
+    },
+    {
+      "name": "Route /settings (设置)",
+      "path": ".next/static/chunks/app/(app)/settings/**/*.js",
+      "limit": "130 KB",
+      "gzip": true
     }
   ]
 }