Accept story 36: Enforce Front Matter on All Story Files

Add POST /workflow/stories/create endpoint that auto-assigns story
numbers, generates correct front matter, and writes to upcoming/.
Add slugify_name and next_story_number helpers with full test coverage.
Add frontend createStory API method and types.
Update README to recommend creation API for agents.

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

frontend/src/api/workflow.ts

@@ -66,6 +66,7 @@ export interface StoryTodosResponse {
 	story_id: string;
 	story_name: string | null;
 	todos: string[];
+	error: string | null;
 }
 
 export interface TodoListResponse {
@@ -75,12 +76,33 @@ export interface TodoListResponse {
 export interface UpcomingStory {
 	story_id: string;
 	name: string | null;
+	error: string | null;
 }
 
 export interface UpcomingStoriesResponse {
 	stories: UpcomingStory[];
 }
 
+export interface StoryValidationResult {
+	story_id: string;
+	valid: boolean;
+	error: string | null;
+}
+
+export interface ValidateStoriesResponse {
+	stories: StoryValidationResult[];
+}
+
+export interface CreateStoryPayload {
+	name: string;
+	user_story?: string | null;
+	acceptance_criteria?: string[] | null;
+}
+
+export interface CreateStoryResponse {
+	story_id: string;
+}
+
 const DEFAULT_API_BASE = "/api";
 
 function buildApiUrl(path: string, baseUrl = DEFAULT_API_BASE): string {
@@ -160,4 +182,18 @@ export const workflowApi = {
 	getStoryTodos(baseUrl?: string) {
 		return requestJson<TodoListResponse>("/workflow/todos", {}, baseUrl);
 	},
+	validateStories(baseUrl?: string) {
+		return requestJson<ValidateStoriesResponse>(
+			"/workflow/stories/validate",
+			{},
+			baseUrl,
+		);
+	},
+	createStory(payload: CreateStoryPayload, baseUrl?: string) {
+		return requestJson<CreateStoryResponse>(
+			"/workflow/stories/create",
+			{ method: "POST", body: JSON.stringify(payload) },
+			baseUrl,
+		);
+	},
 };