feat(11.1-04): add the Backend section, the remaining Services pages and the concept map links

- docs/backend: admin controllers, forms, lists and filters, relation
  manager, users and permissions, settings, partials and widgets, admin SPA
- docs/services: storage, outbound HTTP, realtime, Web Push, search, parity
  testing and the Frontend and AJAX (not provided) page
- Examples for cabana (with testdata/docs YAML), fetchguard, lighthouse and
  its centrifugo driver, flare, beachcomber and typesense, tide; lighthouse
  and beachcomber TestDocs* regions run on their Postgres harnesses
- concept map rows link their guide pages and the not-provided rows the
  Frontend and AJAX page; index lists Backend, Database and Services
- TestDocsRequiredPages asserts the D-08 section order

cmd/summer/docs_test.go

@@ -109,11 +109,43 @@ var requiredPages = []string{
 	"services/oauth-server",
 	"services/mail",
 	"services/localization",
+	"backend/admin-controllers",
+	"backend/forms",
+	"backend/lists-and-filters",
+	"backend/relation-manager",
+	"backend/users-and-permissions",
+	"backend/settings",
+	"backend/partials-and-widgets",
+	"backend/admin-spa",
+	"services/storage",
+	"services/outbound-http",
+	"services/realtime",
+	"services/push",
+	"services/search",
+	"services/parity-testing",
+	"services/frontend-and-ajax",
 }
 
+// sectionOrder is the D-08 sidebar order: WinterCMS's documentation order,
+// with the API reference last.
+var sectionOrder = []string{"setup", "architecture", "plugins", "backend", "database", "services", "console", "api"}
+
 // TestDocsRequiredPages asserts that every required page is in the loaded
-// tree and is built as both .html and .md on the real tree.
+// tree and is built as both .html and .md on the real tree, and that
+// site.yaml lists the sections in sectionOrder.
 func TestDocsRequiredPages(t *testing.T) {
+	raw, err := os.ReadFile(filepath.Join(repoRoot, "docs", "site.yaml"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var sections []string
+	for _, m := range regexp.MustCompile(`(?m)^  - name: (\S+)$`).FindAllStringSubmatch(string(raw), -1) {
+		sections = append(sections, m[1])
+	}
+	if !slices.Equal(sections, sectionOrder) {
+		t.Errorf("site.yaml sections = %v, want %v", sections, sectionOrder)
+	}
+
 	pages, problems, err := docsite.Pages(docsite.Options{Root: repoRoot, Commands: docsCommands()})
 	if err != nil || len(problems) > 0 {
 		t.Fatalf("Pages: %v %v", err, problems)