Avoid mutating image qualities during validation (#99476)
## Summary
Allow the internal blur quality directly during development image
request validation instead of appending it to `images.qualities`. This
preserves quality validation while removing another runtime config
mutation as part of supporting immutable configuration in Vercel adapter
deployments.
## Verification
Existing HTTP tests in `test/e2e/image-optimizer/sharp.test.ts` cover
blur SVG responses, allowed image requests, and rejection of
unconfigured qualities. The four selected cases pass in Turbopack
development, Webpack development, and Webpack production modes.
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