fix: show proper error messages in speaking script generation instead of empty []

Made-with: Cursor

src/pages/GenerationPage.tsx

@@ -294,10 +294,18 @@ export default function GenerationPage() {
     mutationFn: (params: { topics: string[]; difficulty: string; partIndex: number }) =>
       generationService.generateSpeakingScript({ topics: params.topics.filter(Boolean), difficulty: params.difficulty, part: "speaking_1" }),
     onSuccess: (res, vars) => {
+      const r = res as Record<string, unknown>;
+      if (r.error) {
+        toast({ variant: "destructive", title: "Script generation failed", description: String(r.error) });
+        return;
+      }
       const st = getModuleState("speaking");
       const parts = [...st.speakingParts];
-      const r = res as Record<string, unknown>;
-      const script = (r.script as string) ?? JSON.stringify(r.questions ?? res);
+      const script = (r.script as string) || "";
+      if (!script) {
+        toast({ variant: "destructive", title: "No script returned", description: "AI returned empty response — try again." });
+        return;
+      }
       parts[vars.partIndex] = { ...parts[vars.partIndex], script };
       updateModuleState("speaking", { speakingParts: parts });
       toast({ title: "Script generated" });