fix: SkillsUsage 页面样式修复与 API server skill usage 统计 (#698)

* Reapply "feat: 新增 Skills Usage 监控统计与图表 (#668)" (#670)

This reverts commit 91de3b12a1.

* fix: count API-server skill usage

* fix: align SkillsUsageView header with other pages and update sidebar icon

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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Co-authored-by: Zhicheng Han <zhicheng.han@mathematik.uni-goettingen.de>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

packages/server/src/routes/hermes/skills.ts

@@ -4,6 +4,7 @@ import * as ctrl from '../../controllers/hermes/skills'
 export const skillRoutes = new Router()
 
 skillRoutes.get('/api/hermes/skills', ctrl.list)
+skillRoutes.get('/api/hermes/skills/usage/stats', ctrl.usageStats)
 skillRoutes.put('/api/hermes/skills/toggle', ctrl.toggle)
 skillRoutes.put('/api/hermes/skills/pin', ctrl.pin_)
 skillRoutes.get('/api/hermes/skills/:category/:skill/files', ctrl.listFiles)