Burst capacity tested at 10x normal volume

Queue workers that have never been tested at above-normal volume reveal their breaking points in production: the rate limiter was set to a library default, concurrency was never tuned, and the ESP starts returning 429s at 3x normal volume. ISO 25010 reliability.fault-tolerance requires that the system behaves predictably under adverse load conditions. Without a burst test script that runs against a sandbox ESP at 10x normal volume, the concurrency and rate limiter values are guesses — and the first real burst is the test.

Add a burst test script to the repository (e.g., scripts/burst-test.ts) that enqueues 10x normal daily volume against the ESP sandbox:

const NORMAL_DAILY = 10_000
const BURST_MULTIPLIER = 10

for (let i = 0; i < NORMAL_DAILY * BURST_MULTIPLIER; i++) {
  await queue.add('send-email', {
    to: `burst-test-${i}@example.com`,
    template: 'burst-test'
  })
}

console.log(`Enqueued ${NORMAL_DAILY * BURST_MULTIPLIER} jobs. Monitor queue depth and ESP rate.`)

Set explicit concurrency and rate limiter values — not library defaults — before running. After the test, document peak memory usage, time to drain, and any rate limit errors observed.