perf(storybook): scope the renderer matrix to slot-owning stories

[woksin]

Summary

test-storybook ran every indexed story against all four renderer previews (built-in, MUI, PrimeReact 11, PrimeReact 10) in both appearances with axe, even though only components that participate in the renderer slot system can render differently between them. This scopes the renderer dimension to what it can actually distinguish: a story runs the full four-renderer matrix only if its component owns a renderer slot, or transitively composes one; everything else runs once, on the built-in renderer, in both appearances, still with axe.

Measured locally (yarn build && yarn verify-indexes && yarn test-storybook, same checkout, before/after this change):

	Cases	Duration
Before	4 previews × 326 stories × 2 appearances = 2608	83s
After	1 built-in × 326 stories + 3 renderer-distinguishing previews × 175 matrix stories, × 2 appearances = 1702	60s

No consumer-visible change — no-release.

Changed

• test-storybook now runs the full built-in/MUI/PrimeReact 11/PrimeReact 10 matrix only for the 175 of 326 stories whose component owns or composes a renderer slot; the remaining 151 stories run once, on the built-in renderer, in both appearances, still with axe (The story matrix runs four renderers over components that only one renderer can render #302)
• verify-storybook-indexes.mjs now pins the derived slot-owning module count (14) and matrix story count (175) alongside the existing 326 story / 74 docs pins (The story matrix runs four renderers over components that only one renderer can render #302)

Added

• Storybook/scripts/lib/renderer-matrix-scope.mjs derives the renderer-matrix partition automatically: the slot registry comes from a source scan for unstable_useSlot( call sites (the same mechanism RendererContext resolves against), each story's component is read from the already-built Storybook index, and reachability to a slot-owning module follows the local import graph — so a composite like CommandDialog or DataPage that renders a slotted primitive inside it stays in the matrix automatically, and a newly slotted component joins it the moment it starts using unstable_useSlot (The story matrix runs four renderers over components that only one renderer can render #302)
• Storybook/for_renderer_matrix_scope spec covering known built-in-only components (ComboBox, ToggleGroup, Tabs, TagGroup, Breadcrumbs), known composites (CommandDialog, DataPage, ColumnFilterMenu, SchemaEditor), and a regression fixture for a traversal defect caught while writing this derivation (The story matrix runs four renderers over components that only one renderer can render #302)

Notes for reviewers

• Full automatic derivation was achievable here — there is no hand-maintained component list to go stale. As a safeguard against the derivation itself silently regressing (for example, if the unstable_useSlot scan started matching nothing after a rename, which would quietly send every story down the built-in-only path), verify-storybook-indexes.mjs pins the derived counts and fails loudly if they drift, and the new spec exercises known matrix/built-in-only cases directly.
• The reachability walk follows type-only imports the same as value imports, so it can only over-include a story (safe direction), never drop one that genuinely composes a slotted primitive.
• Storybook/preview/main.ts's stories field now accepts an optional CRATIS_STORYBOOK_MATRIX_STORY_GLOBS env override, set by run-story-matrix.mjs for the non-built-in adapter runs only. This goes through Storybook's own stories config rather than Vitest's test.include, because the Storybook Vitest plugin unconditionally overwrites test.include.
• Verified cd Source && yarn ci still passes unchanged.