[Feature] Low-resource upload mode: automatically pause processing during uploads

The feature Add an optional low-resource upload mode for small, HDD-backed, or CPU/RAM-constrained Immich servers. When normal asset uploads are active, Immich should temporarily pause ordinary processing queues, then automatically resume them after a configurable idle delay. The intent is to stop upload writes from competing with thumbnails, metadata extraction, transcodes, OCR, face detection, and similar work on the same disk. Suggested settings: • Enable/disable low-resource upload mode. • Maximum simultaneous asset uploads (for example, 1). • Idle delay before processing resumes (for example, 5 seconds). • Explicit protection for system-maintenance queues, so they are never accidentally left paused. • Clear status logs, such as IMMICH UPLOAD: <user> — upload started and upload finished. This must work with the normal web uploader and normal mobile backup, without a separate import tool or a manual pause/resume workflow. Wh…