feat: add diagnostic web app shell

internal/httpapi/handler.go

@@ -10,6 +10,7 @@ import (
 	"tutor/internal/ontology"
 	"tutor/internal/progression"
 	"tutor/internal/teachingassets"
+	"tutor/internal/webapp"
 )
 
 type Handler struct {
@@ -52,6 +53,7 @@ func (h Handler) Routes() http.Handler {
 	mux.HandleFunc("GET /api/v1/ontology", h.getOntology)
 	mux.HandleFunc("POST /api/v1/teaching-assets/prompts", h.generateTeachingAssetPrompt)
 	mux.HandleFunc("GET /api/v1/teaching-assets", h.getTeachingAssets)
+	mux.Handle("GET /", webapp.Handler())
 	return mux
 }
 

internal/httpapi/handler_test.go

@@ -50,3 +50,28 @@ func TestHealth(t *testing.T) {
 		t.Fatalf("body.ModelKey = %q", body.ModelKey)
 	}
 }
+
+func TestWebAppRoute(t *testing.T) {
+	cfg := config.Config{
+		Environment: "test",
+		ModelKey:    "deepseek-v4-flash",
+	}
+	memory := learnermemory.NewService(learnermemory.NewMemoryStore())
+	service := interview.NewService(interview.NewMemoryStore(), workflows.NewStubRunner(), memory)
+	progress := progression.NewService(memory)
+	onto := ontology.NewService(ontology.NewMemoryStore())
+	assets := teachingassets.NewService(teachingassets.NewMemoryStore(), onto, cfg.ImageModelKey)
+	handler := NewHandler(cfg, service, memory, progress, onto, assets)
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	rec := httptest.NewRecorder()
+
+	handler.Routes().ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
+	}
+	if rec.Header().Get("Content-Type") != "text/html; charset=utf-8" {
+		t.Fatalf("content-type = %q", rec.Header().Get("Content-Type"))
+	}
+}