fix: align frontend referenced_knowledge type with backend dict[str, list[str]]

Closes #38

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: etoyama

frontend/e2e/fixtures/mock-data.ts

@@ -15,7 +15,7 @@ export interface Design {
   chart: Record<string, unknown>[];
   source_ids: string[];
   next_action: Record<string, unknown> | null;
-  referenced_knowledge: Record<string, unknown>[] | null;
+  referenced_knowledge: Record<string, string[]>;
   created_at: string;
   updated_at: string;
 }
@@ -34,7 +34,7 @@ export function makeDesign(overrides?: Partial<Design>): Design {
     chart: [],
     source_ids: [],
     next_action: null,
-    referenced_knowledge: null,
+    referenced_knowledge: {},
     created_at: "2026-01-01T00:00:00",
     updated_at: "2026-01-01T00:00:00",
     ...overrides,

frontend/src/types/api.ts

@@ -84,7 +84,7 @@ export interface Design {
   methodology: Methodology | null;
   source_ids: string[];
   next_action: Record<string, unknown> | null;
-  referenced_knowledge: Record<string, unknown>[] | null;
+  referenced_knowledge: Record<string, string[]>;
   created_at: string;
   updated_at: string;
 }