Replaces the T20 stub. WalkPage dispatches by session_kind:
- 'flow' / 'proposal' → L1WalkTreeVariant (this commit)
- 'adhoc' → placeholder until T23
L1WalkTreeVariant: sticky header with back link + AI-built badge +
persistent Escalate/Resolve buttons; two-pane body (current step
yes/no card on left, walked-path transcript on right). ResolveModal
and EscalateModal extracted to shared WalkModals.tsx (T23 reuses).
Phase 1 caveat: this surface isn't reached by user-driven intake
(which creates adhoc sessions only). It's exercised via direct URL
or integration tests until Phase 2 wires match_or_build.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
