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/[id].patch.ts

@@ -0,0 +1,15 @@
+import { listPromptSequences, updatePromptSequence } from '~/server/utils/promptSequences'
+
+export default defineEventHandler(async (event) => {
+  const { owner } = assertLibraryOwner(event)
+  const id = String(getRouterParam(event, 'id') || '')
+  const body = await readBody<{ name?: string; scenes?: unknown }>(event).catch(() => ({}))
+  const sequence = await updatePromptSequence(owner, id, {
+    name: body?.name,
+    scenes: body?.scenes
+  })
+  return {
+    sequence,
+    sequences: listPromptSequences(owner)
+  }
+})