fix(web): keep subagent rows visible under folded turns - #11474

Eligibility
This is a small, self-contained chat timeline fix that changes only how settled subagent rows participate in visual turn folding. The focused tests cover direct, workflow, active, settled, and unknown-liveness cases, with no schema, infrastructure, security, billing, or static-analysis changes.

Notes:
No code owners found in target merge base c0ddfb3