fix: thread_closed uses chat-clock time, not wall clock (T80.4)

T58 stamped emitted ``thread_closed`` events with
``datetime.now(timezone.utc).isoformat()``. The rest of the close
pipeline (memories.chat_clock_at, scene_closed.ended_at, edge writes)
uses the chat's in-world clock. Threads must agree so timeline
reconstruction stays consistent under time skips and replay.

Read ``chat["time"]`` (already loaded for the per-POV path) and pass
it through as ``closed_at``. Falls back to UTC now only when chat_state
has no clock yet — defensive; chat_created always seeds it.

Adds test_thread_closed_uses_chat_clock_time.

chat/services/scene_summarize.py

@@ -624,12 +624,20 @@ async def apply_scene_close_summary(
                 },
             )
         elif cand.action == "close" and cand.existing_thread_id:
+            # T80.4: chat-clock time, not wall clock — the rest of the
+            # close pipeline (memories, edges, scene_closed payloads)
+            # uses chat["time"] so threads must agree. Falls back to
+            # UTC now only when the chat row has no clock yet (defensive
+            # — chat_state always seeds "time" via chat_created).
+            chat_clock_at = chat.get("time") or datetime.now(
+                timezone.utc
+            ).isoformat()
             append_and_apply(
                 conn,
                 kind="thread_closed",
                 payload={
                     "thread_id": cand.existing_thread_id,
-                    "closed_at": datetime.now(timezone.utc).isoformat(),
+                    "closed_at": chat_clock_at,
                 },
             )