feat: 状态栏支持 refreshInterval 定时刷新

- Zod schema 补齐 refreshInterval 字段
- 通过 scheduleUpdate 复用 300ms debounce，event/settings/time 三路触发单飞
- 新增 docs/features/status-line.mdx 调研文档

src/utils/settings/types.ts

@@ -552,6 +552,7 @@ export const SettingsSchema = lazySchema(() =>
           type: z.literal('command'),
           command: z.string(),
           padding: z.number().optional(),
+          refreshInterval: z.number().optional(),
         })
         .optional()
         .describe('Custom status line display configuration'),