feat: image core — format math, sharp pipeline, sticker contour, prompts, pg-boss queue+worker

- format.ts: exact px (cm/2.54*dpi), catalog incl. The Frame/portrait, aspect ratio
- pipeline.ts: finalizeToFormat (cover/attention crop, dpi metadata), stickerContour
  (alpha dilation -> white border), heic->png, german filename slug
- prompts.ts: task prompts (clean/cutout/format) — reproduce, don't reinterpret
- process.ts: per-item chain (load -> model /v1/images -> finalize -> contour -> store)
- queue.ts + worker.ts: pg-boss (concurrency, retry, counters, 402 pause, completion)
- verified locally: 30x40@300dpi = exact 3543x4724 + dpi meta; sticker white border + alpha

src/lib/queue.ts

@@ -0,0 +1,34 @@
+import PgBoss from 'pg-boss';
+
+export const QUEUE = 'generate';
+export interface GenerateJob { itemId: string; jobId: string; }
+
+let boss: PgBoss | null = null;
+
+export async function getBoss(): Promise<PgBoss> {
+  if (!boss) {
+    boss = new PgBoss({ connectionString: process.env.DATABASE_URL });
+    boss.on('error', (e) => console.error('[pg-boss]', e));
+    await boss.start();
+    await boss.createQueue(QUEUE);
+  }
+  return boss;
+}
+
+export async function enqueue(job: GenerateJob): Promise<void> {
+  const b = await getBoss();
+  await b.send(QUEUE, job, { retryLimit: 2, retryBackoff: true });
+}
+
+export async function startWorker(
+  concurrency: number,
+  handler: (job: GenerateJob) => Promise<void>,
+): Promise<void> {
+  const b = await getBoss();
+  await b.work<GenerateJob>(
+    QUEUE,
+    { batchSize: Math.max(1, concurrency), pollingIntervalSeconds: 2 },
+    async (jobs) => { await Promise.all(jobs.map((j) => handler(j.data))); },
+  );
+  console.log(`[queue] Worker aktiv (Parallelität ${concurrency}).`);
+}