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

modules/lighthouse/export_docs_test.go

@@ -0,0 +1,19 @@
+package lighthouse
+
+import (
+	"testing"
+
+	"git.golem15.com/golem15/summercms/modules/backpack"
+	"gorm.io/gorm"
+)
+
+// DocsEnv returns an app with the memory driver on a fresh migrated
+// database of this package's Postgres harness, with a job worker running,
+// for the database-backed docs examples in example_test.go. It skips under
+// -short and fails when the harness has no database, like the package's
+// other database tests.
+func DocsEnv(t *testing.T) (*backpack.App, *Service, *gorm.DB) {
+	t.Helper()
+	env := newLHEnv(t, nil, nil)
+	return env.app, env.svc, env.gdb
+}