Story 28: Show remaining test TODOs in the UI

Add TodoPanel that displays unchecked acceptance criteria from current
story files. Backend parses `- [ ]` lines from markdown, frontend
shows them in a panel with refresh. Includes 4 Rust unit tests,
3 Vitest tests, 3 Playwright E2E tests.

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

frontend/src/api/workflow.ts

@@ -62,6 +62,16 @@ export interface ReviewListResponse {
 	stories: ReviewStory[];
 }
 
+export interface StoryTodosResponse {
+	story_id: string;
+	story_name: string | null;
+	todos: string[];
+}
+
+export interface TodoListResponse {
+	stories: StoryTodosResponse[];
+}
+
 const DEFAULT_API_BASE = "/api";
 
 function buildApiUrl(path: string, baseUrl = DEFAULT_API_BASE): string {
@@ -131,4 +141,7 @@ export const workflowApi = {
 			baseUrl,
 		);
 	},
+	getStoryTodos(baseUrl?: string) {
+		return requestJson<TodoListResponse>("/workflow/todos", {}, baseUrl);
+	},
 };