Add support for verification_level in AI Catalog logic, queries, and services

Description:

Implement support for the new verification_level enum in the AI Catalog system to enable tracking and filtering of verified items, following the existing behavior in the CI Catalog.

Scope of work:

• Update Ai::Catalog::ItemsFinder to optionally filter by verification_level.
• Update aiCatalogItems GraphQL query to support an optional verification_level argument.
• Update Ci::Catalog::VerifyNamespaceService to also set the appropriate verification_level for all ai_catalog_items under projects belonging to a verified root namespace (same logic as used for CI components).
• Update the following services to set Item.verification_level correctly when the root namespace is verified:
  • Agents::CreateService
  • Flows::CreateService
• Expose a new verificationLevel field on Types::Ai::Catalog::ItemInterface, using Types::Ci::Catalog::Resources::VerificationLevelEnum.