fix(aibox): batch H audit fixes - subagent cancel propagation, scheduler timeout, exec process-group reaping

Fourth audit round (see docs/reports/aibox_audit_20260817.md §11):
- H1: shared parent cancel event no longer cleared on subagent first think
  (N5 regression); parent-already-cancelled skips subagent start
- M1: /reload_prompts moved off event loop (run_in_executor, N3 sibling)
- M2: skill --help scan prewarmed before serving connections
- M3: scheduler task-level timeout (scheduler.task_timeout, default 600s)
- M4: get_recent_memories(None) capped instead of full-table load
- M5: memo delete now physically removes rows (was complete-only)
- M6: PromptManager.reload builds new list then atomically swaps
- L1-L12: read_file arg coercion, proxy save failure reported, SSE
  utf-8 tolerance, persona realpath check, truncation char boundary,
  compressor div0, skill path quoting, ask_user required, POSIX
  process-group kill (pgid captured at Popen), web scheme whitelist,
  registry redact substring match, Bearer redaction in failover logs

aibox/tools/misc_tools.py

@@ -39,10 +39,13 @@ class AskUserTool(Tool):
                     )
                 }
             },
-            "required": []
+            # L8：此前 required 为空，LLM 不传 question 时 str + None 抛 TypeError
+            "required": ["question"]
         }
 
-    def execute(self, question: str, **kwargs) -> str:
+    def execute(self, question: str = None, **kwargs) -> str:
+        if not question:
+            return "❌ 需要提供问题内容（question 参数）"
         return (
                 "你遇到了想搞清楚的事情: " + question + "\n你现在可以询问用户。"
         )