Server v2.4.4

[psilabs-dev]

Dead Letter Queue

• Add DLX/DLQ via RabbitMQ queue arguments; failed tasks that exhaust retries are routed automatically
• Add endpoints to list, inspect, replay, and purge dead-lettered messages
• Add DLQ_DEPTH Prometheus gauge

Priority Queues

• Enable broker-level priority (1–3) on the main task queue
• Add optional priority parameter to all download and metadata endpoints

Worker

• Restructure worker from single module into package with per-domain task modules
• Clean up legacy queue and exchange declarations on worker startup
• Add dev-mode tasks (long-running, failing, retryable) gated behind PIXIVUTIL_SERVER_ENV=development

Metrics

• Extract periodic metrics collection from app.py into PixivServer/service/metrics.py

Client

• Add DLQ client methods and priority parameter to existing methods

Fixes

• Fix potential UnboundLocalError in repository methods by initializing cursor before try blocks
• Fix type annotations in SubscriptionRepository

Infrastructure

• Update PixivUtil2 submodule to server-mode v0.2.0
• Add Celery config unit tests