feat: 添加管理员模型配置页面与 config.yaml 模型管理 API

新增 /api/admin/models 路由（读写 config.yaml models 段、连接测试、写前备份），以及工作区「模型配置」管理页与侧栏入口。

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitignore

@@ -80,8 +80,11 @@ offline-backend-20260512/backend/skill_evolution.json
 skills/
 hermes-agent-main/
 .gitignore
-offline-backend-20260512/backend/tests/*
-deploy
+offline-backend-20260512/backend/tests/*
+# Keep the model configuration regression coverage versioned even though
+# this deployment repository otherwise ignores newly added backend tests.
+!offline-backend-20260512/backend/tests/test_model_management.py
+deploy
 .history
 
 # Cloned third-party repos (local only)