feat(query-block): add author filters

[horacioh]

Summary

• Add query block filter support with persisted Author filters across editor and HM block conversion.
• Add an author account picker for query settings and reuse the account tag input in collaborator flows.
• Apply author filters during query resolution before sorting and limiting, with tests for persistence and resolver behavior.
• Document the query block filter model, current scope, and deferred follow-ups.