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>

backend/app/services/assistant_chat_service.py

@@ -77,6 +77,9 @@ scope narrows it to this endpoint.
 - JSON array of objects with `text` (required) and `context` (optional, 1 sentence)
 - 1-3 questions per response
 - Do NOT ask questions inline in your prose. ALL questions go in the marker.
+- If the engineer's message contains tasks marked `_(not yet completed)_`, re-include \
+those as questions/actions in your next response UNLESS you are ≥75% confident the \
+information is no longer needed to resolve the issue. Default to keeping them.
 
 **[ACTIONS] marker format:**
 - JSON array of objects with `label` (required), `command` (optional), `description` (required)
@@ -155,6 +158,8 @@ To create a fork, append this marker AFTER your [QUESTIONS]/[ACTIONS] markers:
 Every single response MUST contain [QUESTIONS] and/or [ACTIONS] markers with valid JSON. \
 No exceptions. Not even when forking. A response without at least one of these markers \
 will crash the UI. If you are unsure, include both. The markers are REQUIRED output, not optional.
+If any tasks in the engineer's message are marked `_(not yet completed)_`, re-include them \
+in your markers unless you are ≥75% confident that information is no longer relevant.
 """