Read the current implementation and consider the following problem (vibe-kanban 25d8b973)

Currently, the HumanInput node yields a `HumanInputFormFilledEvent` event while form is submmited. However, for form level timeout, current no event about timeout is emitted. This makes the frontend UI not updated while the events of time out are sent to the frontend.

Analysis this problem, propose a way to resolve this issue.

api/core/workflow/node_events/__init__.py

@@ -14,6 +14,7 @@ from .loop import (
 )
 from .node import (
     HumanInputFormFilledEvent,
+    HumanInputFormTimeoutEvent,
     ModelInvokeCompletedEvent,
     PauseRequestedEvent,
     RunRetrieverResourceEvent,
@@ -25,6 +26,7 @@ from .node import (
 __all__ = [
     "AgentLogEvent",
     "HumanInputFormFilledEvent",
+    "HumanInputFormTimeoutEvent",
     "IterationFailedEvent",
     "IterationNextEvent",
     "IterationStartedEvent",

api/core/workflow/node_events/node.py

@@ -56,3 +56,10 @@ class HumanInputFormFilledEvent(NodeEventBase):
     rendered_content: str
     action_id: str
     action_text: str
+
+
+class HumanInputFormTimeoutEvent(NodeEventBase):
+    """Event emitted when a human input form times out."""
+
+    node_title: str
+    expiration_time: datetime