feat(mcp): load MCP servers asynchronously at startup

Boot MCP servers (npx/uvx) on a background thread instead of blocking
agent init. Built-in tools serve traffic immediately while MCP comes
online; each new agent reads whatever is ready at creation time.
Idempotent via _mcp_loaded flag — concurrent sessions never re-fork
subprocesses. Per-server failures are isolated and warmup is triggered
in app.py so loading overlaps with channel startup.

channel/web/static/js/console.js

@@ -50,7 +50,7 @@ const I18N = {
         config_password_hint: '留空则不启用密码保护',
         config_password_changed: '密码已更新，请重新登录',
         config_password_cleared: '密码已清除',
-        skills_title: '技能管理', skills_desc: '查看、启用或禁用 Agent 技能', skills_hub_btn: '探索技能广场',
+        skills_title: '技能管理', skills_desc: '查看、启用或禁用 Agent 工具和技能', skills_hub_btn: '探索技能广场',
         skills_loading: '加载技能中...', skills_loading_desc: '技能加载后将显示在此处',
         tools_section_title: '内置工具', tools_loading: '加载工具中...',
         skills_section_title: '技能', skill_enable: '启用', skill_disable: '禁用',
@@ -149,7 +149,7 @@ const I18N = {
         config_password_hint: 'Leave empty to disable password protection',
         config_password_changed: 'Password updated, please re-login',
         config_password_cleared: 'Password cleared',
-        skills_title: 'Skills', skills_desc: 'View, enable, or disable agent skills', skills_hub_btn: 'Skill Hub',
+        skills_title: 'Skills', skills_desc: 'View, enable, or disable agent tools and skills', skills_hub_btn: 'Skill Hub',
         skills_loading: 'Loading skills...', skills_loading_desc: 'Skills will be displayed here after loading',
         tools_section_title: 'Built-in Tools', tools_loading: 'Loading tools...',
         skills_section_title: 'Skills', skill_enable: 'Enable', skill_disable: 'Disable',