feat(pilot): mount ProposalBanner + wire implicit signals

Replaces the task-lane SuggestedFix card with the ProposalBanner docked
above the chat composer. Wires:
- Resolve-while-verifying auto-marks applied_success (one-click resolve).
- Escalate-while-verifying opens EscalateInterceptDialog to capture the
  real outcome (default: didn't work) before handoff.
- 3+ post-apply engineer messages trigger the passive Nudge banner.
- AI [FIX_OUTCOME] proposals surface in the AIConfirming state; one-click
  confirm applies the outcome.

Banner state resets on session switch via resetSessionDerivedState.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/pilot/ProposalBanner.tsx

@@ -36,7 +36,7 @@ export interface ProposalBannerProps {
   collapsed?: boolean
   onToggleCollapsed?: () => void
   /** Silence the nudge without collapsing it (Task 11 wires this). */
-  onSilenceNudge?: () => void
+  onSilenceNudge: () => void
 }
 
 export function ProposalBanner(props: ProposalBannerProps) {