Add lower-corner layouts, custom blur backgrounds, and classic blur fill.

Ship composition families, optional background images for lower-corner templates, and an optional blurred cover fill for classic letterbox.

app/api/v1/route.ts

@@ -1,4 +1,9 @@
 import { NextResponse } from "next/server";
+import {
+  COMPOSITION_FAMILIES,
+  LAYOUT_TEMPLATE_LABELS,
+  LAYOUT_TEMPLATES,
+} from "@/lib/layout";
 import { API_DOCS_URL } from "@/lib/plans";
 
 export async function GET() {
@@ -17,6 +22,19 @@ export async function GET() {
       batch:
         "POST /api/v1/jobs/batch is for small packs only. Large multipart bodies may fail with 'failed to parse body as FormData'",
     },
+    layoutTemplates: LAYOUT_TEMPLATES.map((id) => ({
+      id,
+      label: LAYOUT_TEMPLATE_LABELS[id],
+    })),
+    compositionFamilies: COMPOSITION_FAMILIES.map((family) => ({
+      id: family.id,
+      label: family.label,
+      defaultTemplate: family.defaultTemplate,
+      variants: family.variants.map((id) => ({
+        id,
+        label: LAYOUT_TEMPLATE_LABELS[id],
+      })),
+    })),
     endpoints: [
       {
         method: "POST",