feat: implement script generation API client function

- Add ScriptSegment, ScriptRequest, and ScriptResponse TypeScript interfaces
- Implement generateScript() function to call /api/tts/script endpoint
- Update GenerateRequest interface to support optional segments array
- Add comprehensive error handling for script generation
- Validates Requirements 15.1, 15.2

frontend/src/api/tts.ts

@@ -29,11 +29,36 @@ export interface RolesResponse {
   roles: Role[];
 }
 
+/**
+ * Represents a script segment with speaker assignment
+ */
+export interface ScriptSegment {
+  id: string;
+  speaker: string;
+  text: string;
+}
+
+/**
+ * Request payload for script generation
+ */
+export interface ScriptRequest {
+  text: string;
+  roles: string[];
+}
+
+/**
+ * Response from the script generation endpoint
+ */
+export interface ScriptResponse {
+  segments: ScriptSegment[];
+}
+
 /**
  * Request payload for audiobook generation
  */
 export interface GenerateRequest {
-  text: string;
+  segments?: ScriptSegment[];
+  text?: string;
   lang: string;
   roles: { id: string; voice: string }[];
   speed?: number;
@@ -188,6 +213,27 @@ export async function detectRoles(text: string): Promise<RolesResponse> {
   return await response.json();
 }
 
+/**
+ * Generate a script preview with AI-segmented text and speaker assignments
+ * @param request - Script request with text and detected roles
+ * @returns Promise resolving to script segments
+ * @throws ApiError if the request fails
+ */
+export async function generateScript(request: ScriptRequest): Promise<ScriptResponse> {
+  const baseUrl = getApiBaseUrl();
+  const url = `${baseUrl}/api/tts/script`;
+  
+  const response = await fetchWithErrorHandling(url, {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+    },
+    body: JSON.stringify(request),
+  });
+  
+  return await response.json();
+}
+
 /**
  * Generate an audiobook from text with assigned voices
  * @param payload - Generation request with text, language, roles, and speed