fix(web): activity rows and chat titles use participant names and the person's first turn (CL-8449)

[TheGreatAxios]

Summary

• Latest activity rows resolve the author through room participants (name, not raw run address), falling back to the address local part only when no participant matches.
• chatTitle now always uses the person's own first turn (never an agent reply); participantAddress falls back to parsing the frame's To: header from raw when envelope.to is empty, so person turns with an empty envelope.to still route into the right chat.
• Verified / still redirects straight to the newest chat with no dialog.

Test plan

• bunx tsc -p apps/web --noEmit
• bun run fmt
• bun run lint
• cd apps/web && bun run build

[linear-code]

CL-8449