feat(search): add locale and facet support

[wsierakowski]

• This PR follows the Contribution Guide
• Changelog updated
• Upgrade guide entry added

Description / Motivation

Adds two new optional capabilities to the Search package backed by the Sitecore Search runtime service:

Locale support — a locale field on SearchParameters (e.g. 'en', 'fr-FR'). Required for multi-locale index configurations; omit for single-locale indexes.

Facet support — a facet field on SearchParameters and facets on SearchResponse, plus six new public types: FacetRequest, FacetField, FacetFilter, FacetFilterOperator, FacetValue, FacetResult. Supports:

• all: true — return counts for every facet enabled in the index configuration
• fields — filter results by specific facet values (string/boolean: eq; numeric/datetime: eq, gt, lt, ge, le)
• Both combined — filter results while still returning full facet counts

Both fields are optional and only sent to the backend when provided (omitempty semantics). Both hooks useSearch and useInfiniteSearch in @sitecore-content-sdk/react are updated accordingly.

Testing Details

• Unit Test Added
• Manual Test/Other

Added 5 unit tests to packages/search/src/search-service.test.ts:

• locale: sends locale when provided, omits it when not provided
• facets: sends facet when provided, maps data.facet → response.facets, omits facet when not provided

API surface files regenerated via npm run api-extractor in both packages/search and packages/react.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

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Latest commit: 4352b4a

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