fix(team-inbox): satisfy React lifecycle rules

[beruro]

Summary

• keep render-time recency grouping pure by passing the successful-load timestamp from the owning view
• derive loading state from a request key instead of synchronously resetting state inside an effect
• capture the realtime teardown map owned by the effect so cleanup does not dereference a changing ref
• add a regression test proving stale Work Item responses cannot replace the current selection

Audits

• Frontend UI: 2 fix, 4 keep with reason, 0 abstract; no sweep candidate
• Performance guard: PASS
  • request work is demand-driven per selected item; no timer or polling added
  • target changes cancel the old effect and stale completions are ignored
  • realtime subscriptions and trailing timers retain explicit teardown
  • repeated open/close cycles retain no component-owned request or listener state

Verification

• Team Inbox focused suite: 30 tests passed
• added stale-response lifecycle test
• tsc --noEmit
• focused ESLint and Prettier checks
• full pnpm run lint
• git diff --check

[beruro]

Obsolete after develop reverted #521. Superseded by #530, which reapplies the complete Team Inbox feature together with these lifecycle fixes on the post-revert develop baseline.