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>

---------

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

packages/client/src/components/layout/AppSidebar.vue

@@ -220,6 +220,12 @@ function openChangelog() {
             </svg>
             <span>{{ t("sidebar.usage") }}</span>
           </button>
+          <button class="nav-item" :class="{ active: selectedKey === 'hermes.skillsUsage' }" @click="handleNav('hermes.skillsUsage')">
+            <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round">
+              <polyline points="22 12 18 12 15 21 9 3 6 12 2 12" />
+            </svg>
+            <span>{{ t("sidebar.skillsUsage") }}</span>
+          </button>
         </div>
       </div>