v2.0.0: 主题系统+SSH私钥解析修复+会话持久化+连接池优化+UI打磨

核心修复:
- ssh-service.ts: 新增 resolvePrivateKey()，将私钥文件路径(~/.ssh/id_rsa)解析为内容后传给 ssh2，
  解决 'Cannot parse privateKey: Unsupported key format' 错误
- useTerminalConnection.ts + sessionHelper.ts: 根据 authType 过滤字段，password/agent 认证不再传 privateKey
- sessionStore.ts: addSession() 现在先调用 sessionCreate() 持久化到 SQLite，解决恢复标签'无可用连接信息'问题
- database-service.ts: updateSession() 补充 private_key_path 字段持久化
- SessionDialog.tsx: 默认 username='root'、privateKey='~/.ssh/id_rsa'

UI/UX:
- 语义化主题系统(app-theme.ts)，强制深色模式，全局无边框设计
- macOS 标题栏支持双击最大化(window:toggleMaximize IPC)
- macOS 菜单栏('OpsXShell' 应用菜单 + Settings Cmd+,)
- WelcomeView 4卡片布局，移除 Settings 按钮
- TabBar/TabItem 背景色统一(bg-dark-800/900)，消除白色边框线

架构优化:
- SFTP 生命周期修复(useSFTP.ts useRef + autoConnectAttempted guard)
- 连接池竞态修复，支持快速多标签连接
- IPC 接口规范化，安全错误处理
- Vite 代码分割优化

质量: lint零错误 | tsc零错误 | build成功 | 49 tests pass

src/components/WelcomeView.tsx

@@ -1,4 +1,4 @@
-import { Terminal, FolderSync, ArrowRightLeft, Globe, Settings, Plus, Zap, Clock } from 'lucide-react'
+import { Terminal, FolderSync, ArrowRightLeft, Globe, Plus, Zap, Clock } from 'lucide-react'
 import { useSessionStore } from '../stores'
 import { useTabStore } from '../stores/tabStore'
 import EmptyState from './common/EmptyState'
@@ -24,17 +24,17 @@ export default function WelcomeView({ onNewSession, onQuickConnect }: WelcomeVie
   }
 
   return (
-    <div className="h-full flex flex-col items-center justify-center bg-dark-900 p-8">
-      <div className="text-center mb-12">
+    <div className="h-full flex flex-col items-center justify-start bg-dark-900 p-8 overflow-y-auto">
+      <div className="text-center mb-12 pt-8">
         <div className="w-20 h-20 bg-dark-700 rounded-2xl flex items-center justify-center mx-auto shadow-lg">
           <Terminal className="w-10 h-10 text-white" />
         </div>
       </div>
 
-      <div className="grid grid-cols-1 sm:grid-cols-2 gap-4 w-full max-w-2xl mb-12">
+      <div className="grid grid-cols-2 gap-4 w-full max-w-2xl mb-12">
         <button
           onClick={onQuickConnect}
-          className="flex items-center gap-4 p-6 bg-dark-800 hover:bg-dark-700 rounded-xl border border-dark-700 hover:border-accent-blue transition-all group"
+          className="flex items-center gap-4 p-6 bg-dark-800 hover:bg-dark-700 rounded-xl border border-dark-700/30 hover:border-accent-blue transition-all group"
         >
           <div className="w-12 h-12 bg-accent-blue/20 rounded-lg flex items-center justify-center group-hover:bg-accent-blue/30 transition-colors">
             <Zap className="w-6 h-6 text-accent-blue" />
@@ -47,7 +47,7 @@ export default function WelcomeView({ onNewSession, onQuickConnect }: WelcomeVie
 
         <button
           onClick={onNewSession}
-          className="flex items-center gap-4 p-6 bg-dark-800 hover:bg-dark-700 rounded-xl border border-dark-700 hover:border-accent-green transition-all group"
+          className="flex items-center gap-4 p-6 bg-dark-800 hover:bg-dark-700 rounded-xl border border-dark-700/30 hover:border-accent-green transition-all group"
         >
           <div className="w-12 h-12 bg-accent-green/20 rounded-lg flex items-center justify-center group-hover:bg-accent-green/30 transition-colors">
             <Plus className="w-6 h-6 text-white" />
@@ -60,7 +60,7 @@ export default function WelcomeView({ onNewSession, onQuickConnect }: WelcomeVie
 
         <button
           onClick={() => addTab({ title: 'SFTP', type: 'sftp' })}
-          className="flex items-center gap-4 p-6 bg-dark-800 hover:bg-dark-700 rounded-xl border border-dark-700 hover:border-accent-purple transition-all group"
+          className="flex items-center gap-4 p-6 bg-dark-800 hover:bg-dark-700 rounded-xl border border-dark-700/30 hover:border-accent-purple transition-all group"
         >
           <div className="w-12 h-12 bg-accent-purple/20 rounded-lg flex items-center justify-center group-hover:bg-accent-purple/30 transition-colors">
             <FolderSync className="w-6 h-6 text-accent-purple" />
@@ -73,7 +73,7 @@ export default function WelcomeView({ onNewSession, onQuickConnect }: WelcomeVie
 
         <button
           onClick={() => addTab({ title: '端口转发', type: 'portforward' })}
-          className="flex items-center gap-4 p-6 bg-dark-800 hover:bg-dark-700 rounded-xl border border-dark-700 hover:border-accent-orange transition-all group"
+          className="flex items-center gap-4 p-6 bg-dark-800 hover:bg-dark-700 rounded-xl border border-dark-700/30 hover:border-accent-orange transition-all group"
         >
           <div className="w-12 h-12 bg-orange-500/20 rounded-lg flex items-center justify-center group-hover:bg-orange-500/30 transition-colors">
             <ArrowRightLeft className="w-6 h-6 text-orange-400" />
@@ -83,19 +83,6 @@ export default function WelcomeView({ onNewSession, onQuickConnect }: WelcomeVie
             <div className="text-sm text-gray-500">本地/远程/SOCKS5 代理</div>
           </div>
         </button>
-
-        <button
-          onClick={() => addTab({ title: '设置', type: 'settings' })}
-          className="flex items-center gap-4 p-6 bg-dark-800 hover:bg-dark-700 rounded-xl border border-dark-700 hover:border-gray-500 transition-all group"
-        >
-          <div className="w-12 h-12 bg-gray-700/50 rounded-lg flex items-center justify-center group-hover:bg-gray-700 transition-colors">
-            <Settings className="w-6 h-6 text-gray-400" />
-          </div>
-          <div className="text-left">
-            <div className="font-semibold text-gray-200">设置</div>
-            <div className="text-sm text-gray-500">配置应用偏好</div>
-          </div>
-        </button>
       </div>
 
       {/* Recent connections */}
@@ -113,7 +100,7 @@ export default function WelcomeView({ onNewSession, onQuickConnect }: WelcomeVie
               <button
                 key={session.id}
                 onClick={() => handleSessionClick(session)}
-                className="w-full flex items-center justify-between p-4 bg-dark-800 hover:bg-dark-700 rounded-lg border border-dark-700 hover:border-accent-blue/50 transition-colors"
+                className="w-full flex items-center justify-between p-4 bg-dark-800 hover:bg-dark-700 rounded-lg border border-dark-700/30 hover:border-accent-blue/50 transition-colors"
               >
                 <div className="flex items-center gap-3">
                   <Globe className="w-5 h-5 text-accent-blue" />