feat(portal-shell): restore codegen typescript-operations for data-ana domain (P1-7)

ARCHITECTURE.md §10 P1-7: dashboard domain's 6 operations strictly
match the schema, so disable skipDocumentsValidation for that output
and restore per-operation type generation.

Changes:
- codegen.yml: add dashboard-types.ts output (typescript +
  typescript-operations plugins, skipDocumentsValidation: false);
  move documents config into each generates entry
- dashboard.ts: remove 14 handwritten interfaces and 6 internal query
  type aliases; derive types via NonNullable<GetXxxQuery['xxx']> so
  the public hook API shape stays unchanged
- admin/student/teacher page.tsx: add ?? "--" / ?? 0 null guards on
  StatCard value props to match schema nullable semantics (parent page
  already uses toFixed chain, no change needed)

Acceptance (ARCHITECTURE.md §10 P1-7):
- codegen 3 outputs all SUCCESS
- tsc 0 errors / eslint 0 errors / vitest 231 passed / next build ok
- 6 operations strictly match schema with 0 errors

Refs: ARCHITECTURE.md §5.3 data layer / §10 P1-7

apps/portal-shell/src/app/shell/admin/page.tsx

@@ -49,15 +49,19 @@ export default function AdminDashboardPage(): React.ReactElement {
       description="全校概览"
       stats={
         <>
-          <StatCard title="教师总数" value={data.total_teachers} icon={Users} />
+          <StatCard
+            title="教师总数"
+            value={data.total_teachers ?? "--"}
+            icon={Users}
+          />
           <StatCard
             title="学生总数"
-            value={data.total_students}
+            value={data.total_students ?? "--"}
             icon={GraduationCap}
           />
           <StatCard
             title="班级总数"
-            value={data.total_classes}
+            value={data.total_classes ?? "--"}
             icon={Building2}
           />
           <StatCard