feat: 工具执行超时可配置 + 修复硬编码盖过工具自定义超时的 bug

1. 新增 agent.toolExecutionTimeoutMs 配置（默认 120s，范围 10~600s），AgentSettings 加输入框

2. 修复 engine.ts 硬编码 120s 会盖过 delegate-task(5min)/web-search(5min) 等工具自定义 timeoutMs 的 bug：改为取 max(配置值, tool.timeoutMs)

3. main.ts 启动时从 ConfigService 加载；handlers.ts 监听 config:set 即时更新

src/components/settings/SettingsModal.tsx

@@ -369,6 +369,7 @@ function AgentSettings() {
   const [thinking, setThinking] = useConfig('agent.enableThinking', true);
   const [thinkingEffort, setThinkingEffort] = useConfig('agent.thinkingEffort', 'high');
   const [confirmTimeout, setConfirmTimeout] = useConfig('agent.confirmationTimeoutMs', 120000);
+  const [toolExecTimeout, setToolExecTimeout] = useConfig('agent.toolExecutionTimeoutMs', 120000);
 
   const MAX_ITER_OPTIONS = [10, 20, 50, 85, 128, 256, 512];
 
@@ -394,6 +395,18 @@ function AgentSettings() {
         }}
         slotProps={{ htmlInput: { min: 120, max: 3600, step: 30 } }}
       />
+      <TextField
+        size="small"
+        label="工具执行超时（秒）"
+        type="number"
+        value={toolExecTimeout / 1000}
+        onChange={(e) => {
+          const v = Number(e.target.value);
+          if (v >= 10 && v <= 600) setToolExecTimeout(v * 1000);
+        }}
+        slotProps={{ htmlInput: { min: 10, max: 600, step: 10 } }}
+        helperText="单个工具执行的最大时长，超时自动终止（10~600 秒）"
+      />
       <TextField
         size="small"
         label="工具确认超时（秒）"