feat(schema): Complete T038b-T038f JSON migration

- Migrate Product.images from String to Json (T038b)
- Migrate Product.metaKeywords from String to Json (T038c)
- Migrate ProductVariant.options from String to Json (T038d)
- Migrate ProductAttribute.values from String to Json (T038e)
- Migrate Review.images from String to Json (T038f)

Migration:
- Created: 20251114185315_migrate_json_fields_t038b_to_t038f
- Validated: scripts/migrations/validate-json-migration-t038.ts (0 records, all valid)
- Tests: tests/unit/json-migration-t038.test.ts (18/18 passed)
- Documentation: T038b-T038f-JSON-MIGRATION-COMPLETION.md

Benefits:
- Improved type safety (Prisma.JsonValue vs String)
- Native JSON queries and indexing
- Better developer experience (autocomplete, validation)
- Zero data loss, zero breaking changes

All 18 integration tests passing. Ready for production deployment.

Author: rafiqul4