Gateway: regen/proxy updates for Activity list proto changes (incl. ListOrganizationThreads)

[rowan-stein]

User request

Update Gateway to reflect the API changes required for server-side Activity lists (Workloads/Storage/Threads), primarily via regeneration/proxy wiring.

Source spec: https://github.com/agynio/architecture/blob/main/changes/2026-04-24-activity-server-side-lists.md

Specification (architecture/product)

Gateway is a thin proxy; enforcement happens in backend services. After agynio/api updates:

• Gateway must expose updated Runners list shapes.
• Gateway must expose the new Threads ListOrganizationThreads RPC (while keeping existing RPCs for compatibility as needed).

Work items

• Update dependency on buf.build/agynio/api (update buf.lock).
• Regenerate Gateway code from updated protos.
• Ensure the Gateway service includes/connects handlers for any newly added RPCs (especially Threads.ListOrganizationThreads).
• Run tests / build checks.

Acceptance

• Gateway builds cleanly against the updated API module.
• New RPCs are exposed and correctly proxied.