Add image support for productBrand query

[cgarempire]

Summary

• add ProductBrand.image as a nullable MediaItem field
• resolve brand images from WooCommerce term thumbnail_id meta, matching existing ProductCategory.image behavior
• add wpunit coverage for single brand and root productBrands queries

Validation

• ProductBrandQueriesTest: OK (9 tests, 33 assertions)
• ProductCategoryQueriesTest: OK (4 tests, 15 assertions)
• vendor/bin/phpcs -vp .: OK
• vendor/bin/phpstan analyze --ansi --memory-limit=4G: OK

Notes

ProductCategory.image already exists, so this PR only brings ProductBrand to parity with the existing category image field.

[kidunot89]

Looks good. Thanks for the contribution 🙏🏿

[coveralls]

Coverage Report for CI Build 28451865481

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage increased (+0.008%) to 91.809%

Details

• Coverage increased (+0.008%) from the base build.
• Patch coverage: 19 of 19 lines across 3 files are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	20205
Covered Lines:	18550
Line Coverage:	91.81%
Coverage Strength:	153.69 hits per line

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💛 - Coveralls