Standalone dialog (app-dialog, size lg) reusing MediaLibraryFacade so it
shares the exact same asset list/search/pagination/upload state as the
Media Manager page. Emits (selected) with the chosen MediaAsset and
(closed) to dismiss - selecting a tile emits both.
Completes Sprint 4 (Media Manager): ADR-0002 contract, MediaRepository +
mock IndexedDB adapter, Media Manager UI, reusable Media Picker.
Not yet wired into Product Editor or Static Pages editor - that's the
next natural step when those features gain image fields, not part of
this sprint's scope.
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