fix: resolve task lane stale state, partial submit, and closure bugs

- Import and call clearTaskState before updating questions/actions in
  handleSend and handleTaskSubmit so new AI tasks always replace stale
  sessionStorage cache instead of being overridden by it
- Include pending (not yet completed) tasks in the AI message on partial
  submit so the AI knows which tasks were left unanswered
- Fix stale closure in TaskLane saveTaskLane useEffect — use refs for
  questions/actions so the debounced backend save always uses current values
- Add responses field to pending_task_lane TypeScript type, removing the
  unsafe double-cast in selectChat
- Instruct the AI to re-surface incomplete tasks unless ≥75% confident
  the information is no longer needed

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

frontend/src/types/ai-session.ts

@@ -196,7 +196,7 @@ export interface AISessionDetail extends AISessionSummary {
   ticket_data: Record<string, unknown> | null
   steps: AISessionStepResponse[]
   conversation_messages: Array<{ role: string; content: string }>
-  pending_task_lane: { questions: QuestionItem[]; actions: ActionItem[] } | null
+  pending_task_lane: { questions: QuestionItem[]; actions: ActionItem[]; responses?: Array<Record<string, unknown>> } | null
   is_branching: boolean
   active_branch_id: string | null
 }