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/tide/example_test.go

@@ -0,0 +1,69 @@
+package tide_test
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"os"
+
+	"git.golem15.com/golem15/summercms/modules/tide"
+)
+
+// backend stands in for one implementation of GET /api/blog/posts.
+func backend(body string) *httptest.Server {
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, body)
+	}))
+}
+
+func ExampleReplayFlow() {
+	ctx := context.Background()
+	// The reference (PHP) backend and two Go ports. IDs and *_at timestamps
+	// legitimately differ; the second port changed a title.
+	reference := backend(`{"data":[{"id":12,"title":"Hello","created_at":"2026-09-30T10:00:00+00:00"}]}`)
+	defer reference.Close()
+	port := backend(`{"data":[{"id":3,"title":"Hello","created_at":"2026-10-01T08:30:00+00:00"}]}`)
+	defer port.Close()
+	broken := backend(`{"data":[{"id":3,"title":"hello","created_at":"2026-10-01T08:30:00+00:00"}]}`)
+	defer broken.Close()
+
+	raw, err := os.ReadFile("testdata/docs/posts-spec.yaml")
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	spec, err := tide.ParseFlow(raw)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	// Record the reference once; the flow is what testdata/parity keeps.
+	flow, err := tide.RecordFlow(ctx, spec, tide.RecordConfig{Target: reference.URL})
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	for _, target := range []string{port.URL, broken.URL} {
+		res, err := tide.ReplayFlow(ctx, flow, tide.ReplayConfig{Target: target})
+		var mismatch *tide.MismatchError
+		if errors.As(err, &mismatch) {
+			res = mismatch.Result // a difference is an error carrying the result
+		} else if err != nil {
+			fmt.Println(err)
+			return
+		}
+		fmt.Println("ok:", res.OK)
+		for _, step := range res.Steps {
+			for _, d := range step.Diffs {
+				fmt.Printf("  %s %s: want %s, got %s\n", step.ID, d.Path, d.Expected, d.Actual)
+			}
+		}
+	}
+	// Output:
+	// ok: true
+	// ok: false
+	//   list-posts $.data[0].title: want "Hello", got "hello"
+}