Locks in the fix from #1436: when `metadataBase` is configured (on a parent
layout) and `generateImageMetadata` produces multiple dynamic icon /
apple-icon images, the rendered `<link>` href values must stay relative,
matching Next.js behavior in
test/e2e/app-dir/metadata-dynamic-routes/index.test.ts ("should support
generate multi images with generateImageMetadata").
The existing unit-level coverage in features.test.ts verifies MetadataHead
output directly. This adds an integration test through the full pipeline
(applyFileBasedMetadata -> MetadataHead) covering route groups, dynamic
segments, and parent-layout metadataBase inheritance — the exact shape of
the failing Next.js deploy test in #1493.
Refs #1493