feat: 新增技能置顶功能

- 后端:新增 PUT /skills/custom/{name}/featured 接口,在 usage 中实现 set_featured 与 featured 字段(与 pinned 正交,仅影响排序)
- 前端:新增 setSkillFeatured API、置顶/取消置顶操作及中英文文案
- ScheduledTasksPage:优化助手选择下拉框的宽度与文本换行
- config.yaml:整理 log_system 配置块

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend-web/src/pages/ScheduledTasksPage.tsx

@@ -991,12 +991,12 @@ export default function ScheduledTasksPage() {
               </SelectTrigger>
               <SelectContent
                 position="popper"
-                className="w-[var(--radix-select-trigger-width)] max-w-[var(--radix-select-trigger-width)]"
+                className="max-h-[40vh] w-[max(var(--radix-select-trigger-width),28rem)] max-w-[min(90vw,40rem)]"
               >
                 <SelectItem value="__default__">默认助手（不指定）</SelectItem>
                 {agents.map((agent) => (
                   <SelectItem key={agent.id} value={agent.id}>
-                    <span className="block truncate">
+                    <span className="block whitespace-normal break-words">
                       {desensitize(agent.name)}
                       {agent.description ? ` — ${desensitize(agent.description)}` : ""}
                     </span>