fix: resolve TypeScript errors from cockpit refactor (Phase 7)

- Remove unused imports (ChatMessage, TaskLane)
- Remove unused handleTaskSubmit and handleFlowPilotAnswer
- Remove unused setActiveStepIndex setter
- Add triage fields to AISessionDetail construction in useFlowPilotSession
- npx tsc -b passes clean

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/hooks/useFlowPilotSession.ts

@@ -95,6 +95,11 @@ export function useFlowPilotSession(): UseFlowPilotSession {
         pending_task_lane: null,
         is_branching: false,
         active_branch_id: null,
+        client_name: null,
+        asset_name: null,
+        issue_category: null,
+        triage_hypothesis: null,
+        evidence_items: null,
       })
       setAllSteps([firstStep])
       setCurrentStep(firstStep)