Paint live agents above the prompt

[TheGreatAxios]

Summary

• Live agents render in a chrome strip above the prompt instead of updating inside the chat transcript.
• Completed, failed, and cancelled agent rows linger briefly, then the strip clears when idle.
• Agent rows use primary text styling, cap visible rows at ten, and disclose overflow with a +N more row.
• Live transcript task-row progress rewrites pause while the chrome strip owns live status.

Verification

• bun test src/tui/chrome-state.test.ts src/tui/product-host.test.ts src/tui/runtime-channels.test.ts src/tui/wave6.test.ts
• bun run check (fails in prettier --check with repo-wide formatting warnings outside this PR scope)

Refs CL-6898

[linear-code]

CL-6898