Plumbing for the per-item rendering pass — no UI changes yet, just
the layers the home/playlist/liked migrations will sit on.
* CachedHomeIndex drift table (schema 5→6) — section/position →
entity-id rows, populated by the upcoming /api/home/index endpoint.
* HydrationQueue (concurrency=4, in-flight dedup) — bounded request
pump that takes (entityType, entityId) and persists the result to
the right cached_<entity> table. Albums + artists wired today;
tracks deferred until /api/tracks/:id exists.
* Per-entity tile providers (albumTileProvider, artistTileProvider,
trackTileProvider as StreamProvider.family) — watch drift, enqueue
hydration on miss, yield AsyncValue<EntityRef?>.
* Skeleton widgets (album/artist/track) matched to the real card
dimensions with a 1.2s shimmer sweep using FabledSword tokens. No
shimmer-package dep — single AnimationController per surface.
See docs/superpowers/specs/2026-05-13-per-item-rendering-design.md
for the full architecture rationale.
