fix: raise archive upload limits

[tomvothecoder]

Description

• Raises the backend archive-upload limit to 320 MiB.
• Updates the documented Rancher NGINX Ingress body-size limit to 325m, allowing for multipart upload overhead.
• Updates the oversized-upload test without allocating a large test payload.

Checklist

• Code follows project style guidelines
• Self-reviewed code
• No new warnings
• Tests added or updated (if needed)
• All tests pass (locally and CI/CD) — targeted ingestion test passed locally; CI pending
• Documentation/comments updated (if needed)
• Breaking change noted (if applicable)

Deployment Notes (if any)

Deploy the backend change and set the live Rancher NGINX Ingress annotation:

nginx.ingress.kubernetes.io/proxy-body-size: 325m