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

docs/services/configuration.md

@@ -91,7 +91,7 @@ The application opens its configuration once with `compass.Load("config")` in th
 
 `compass.Config.Set` changes a value in memory. `compass.Config.Persist` saves every value set at runtime to `config/env/<environment>/overrides.yaml`, keeping the keys already saved there. It replaces the file atomically, creates it readable only by its owner and refuses any path outside the config directory. `compass.Config.Reload` rereads every source and discards values that were set but not persisted.
 
-Values that admins edit in the backend are not configuration: settings pages store them in a database row.
+Values that admins edit in the backend are not configuration: settings pages store them in a database row; see [Settings](../backend/settings.md).
 
 > [!WARNING]
 > `overrides.yaml` is written by the running application. Keep it out of version control, and keep secrets in environment variables rather than in values the application persists.