feat: add diagnostic interview loop

internal/interview/catalog.go

@@ -0,0 +1,29 @@
+package interview
+
+import "tutor/internal/workflows"
+
+func BackendDeveloperQuestions() []Question {
+	return []Question{
+		{
+			ID:     "backend-http-idempotency",
+			Prompt: "What makes an HTTP method idempotent, and why does that matter for retries?",
+			Concepts: []workflows.ConceptRef{
+				{ID: "http-idempotency", Label: "HTTP idempotency", Track: BackendDeveloperTrack},
+			},
+		},
+		{
+			ID:     "backend-db-index-tradeoff",
+			Prompt: "When would adding a database index improve an API, and what tradeoffs can it introduce?",
+			Concepts: []workflows.ConceptRef{
+				{ID: "database-indexes", Label: "Database indexes", Track: BackendDeveloperTrack},
+			},
+		},
+		{
+			ID:     "backend-cache-invalidation",
+			Prompt: "How would you decide whether to cache an API response, and how would you handle stale data?",
+			Concepts: []workflows.ConceptRef{
+				{ID: "cache-invalidation", Label: "Cache invalidation", Track: BackendDeveloperTrack},
+			},
+		},
+	}
+}