Add Prompt Builder page for multi-scene prompt sequences.

Name, save, and load ordered scenes on the server; assemble copyable text with a Batch-compatible double blank line between scenes.

server/api/prompt-sequences.get.ts

@@ -0,0 +1,8 @@
+import { listPromptSequences } from '~/server/utils/promptSequences'
+
+export default defineEventHandler((event) => {
+  const { owner } = assertLibraryOwner(event)
+  return {
+    sequences: listPromptSequences(owner)
+  }
+})