feat(ep-commerce): tiered designer data surface for catalog-search (ADR-0011)

[field123]

Summary

Brings the catalog-search components up to the ADR-0006/0007 insulation floor under one governing principle — progressive disclosure: the common case is a discoverable, zero-lookup, zero-wiring action; every advanced path stays reachable underneath; and no enhancement removes a capability (every convenience opt-outs to the exact prior behaviour).

Implements ADR-0011 ("Catalog-search designer ergonomics: a tiered, progressively-disclosed data surface"). Closes #355 (under the #304 umbrella).

Slice 1 — discoverable, tiered hit data surface

• D7 (shared base Product contract): extract the hit normalizer into utils/normalize-hit.ts (normalizeSearchHit → SearchHitProduct extends Product), built from the same primitives the PDP path uses (formatCurrency, buildExtensionsMap, normalizeExtensions). A hit's currentProduct is shape-identical to the PDP's, so the ADR-0006 field components and bindings work unchanged across PDP + search. Absent base fields read as absent (never throw).
• D1 (discoverable hit fields): EPSearchHits publishes per hit
  • Tier 1 — $ctx.currentProduct.fields.<key>: flat, slug-free, null-safe, flattening a configurable primaryExtensionTemplate prop (autocompletes in the picker, no (… || {}), no slug brackets);
  • Tier 2 — $ctx.productExtensions["<slug>"].field: the ADR-0007 slug-keyed Proxy map, scoped per hit;
  • Tier 3 — raw extensions / rawData retained.
• D3 (fields): fold highlight: auto | on | off and a titlecase format into EPProductField — one field-render surface across PDP + search. Only the backend's <mark> markup is ever rendered as HTML, never the raw value, so the html:true footgun is removed rather than handed to designers.
• D8/D9: EPSearchHits ships a batteries-included-but-unstyled default card built from the field components, and collapses to a single render (pure inner fed items, the InstantSearch hook in the data wrapper) per the PRD: EP catalog-search components must honour designer styling (headless styling contract) #305 headless-styling contract.

Slice 2 — zero-wiring facets & pagination

• D2 (auto-wiring): refinement items and single-select items are auto-wired via the prop-getter pattern the autocomplete already uses (onClick + keyboard + role + selection aria-*). A defaulted-on, disableable autoWire prop; OFF is byte-for-byte today's function-on-context behaviour, and toggle stays on context as the escape.
• D5/D6 (EPSingleSelectFacet): new component (useMenu, replace semantics, radiogroup a11y) splitting singleSelect out of EPRefinementList. Per-item context is identical, so slot content ports across a mode change. Opt-in includeAllOption emits an "All" pseudo-item (refined when nothing is, clears on select) flagged isAllOption. EPRefinementList + EPClearRefinements keep working unchanged.
• D4 (pagination windowing): EPSearchPagination exposes a windowed pageItems model — ellipsis sentinels, isFirst/isLast/isCurrent flags, a per-item pre-bound goTo, and a windowSize prop. Raw pages: number[] + goTo retained.

Cross-cutting

• D3 (provider): EPCatalogSearchProvider gains excludeVariationChildren (default on) emitting meta.product_types:!=child, AND'd with baseFilter. Deliberate non-additive default — variation children near-universally don't belong in hits, and the package has no external consumers depending on the old behaviour. Turn off to include them.
• D8 (insert section): every catalog-search component groups under one "EP Catalog Search" insert-menu section; the provider's default slot is a complete, working unstyled scaffold (search box + scope facet + hits + empty + pagination).

Verification

• 1816 package tests pass (catalog-search-components jest suite + new unit/acceptance tests: normalize-hit, pagination-window, product-field-highlight, format-value titlecase, provider excludeVariationChildren, EPSingleSelectFacet).
• assertHeadlessStylingContract passes for the new EPSingleSelectFacet and the refactored EPRefinementList / EPSearchHits.
• tsc --noEmit clean across all touched files.
• All enhancements opt-out to prior behaviour; existing component instances render without re-authoring.

Behaviour change to call out

excludeVariationChildren defaults on — searches that previously returned PXM variation children will stop doing so. This is intentional and documented above; set the prop to false to restore the old behaviour.