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

tailwind.config.js

@@ -4,21 +4,82 @@ export default {
     "./index.html",
     "./src/**/*.{js,ts,jsx,tsx}",
   ],
+  darkMode: 'class',
   theme: {
     extend: {
       colors: {
-        // Background surfaces — driven by CSS custom properties set per theme
+        // Semantic color tokens — driven by CSS custom properties set per theme
+        surface: {
+          base: 'var(--color-surface-base)',
+          raised: 'var(--color-surface-raised)',
+          overlay: 'var(--color-surface-overlay)',
+          inset: 'var(--color-surface-inset)',
+        },
+        // Legacy dark-* aliases for backward compatibility
         dark: {
-          900: 'var(--color-dark-900)',
-          800: 'var(--color-dark-800)',
-          700: 'var(--color-dark-700)',
-          600: 'var(--color-dark-600)',
+          900: 'var(--color-surface-base)',
+          800: 'var(--color-surface-raised)',
+          700: 'var(--color-surface-overlay)',
+          600: 'var(--color-surface-inset)',
         },
         accent: {
           blue:   'var(--color-accent-blue)',
           green:  'var(--color-accent-green)',
           purple: 'var(--color-accent-purple)',
           orange: 'var(--color-accent-orange)',
+          red:    'var(--color-accent-red)',
+        },
+        content: {
+          primary:   'var(--color-content-primary)',
+          secondary: 'var(--color-content-secondary)',
+          tertiary:  'var(--color-content-tertiary)',
+          inverse:   'var(--color-content-inverse)',
+        },
+        border: {
+          DEFAULT: 'var(--color-border)',
+          strong:  'var(--color-border-strong)',
+        },
+      },
+      fontFamily: {
+        sans: [
+          'Inter',
+          '-apple-system',
+          'BlinkMacSystemFont',
+          '"Segoe UI"',
+          'Roboto',
+          '"Helvetica Neue"',
+          'Arial',
+          '"Noto Sans SC"',
+          '"PingFang SC"',
+          '"Microsoft YaHei"',
+          'sans-serif',
+        ],
+        mono: [
+          'Menlo',
+          'Monaco',
+          'Consolas',
+          '"Liberation Mono"',
+          '"Courier New"',
+          'monospace',
+        ],
+      },
+      animation: {
+        'fade-in': 'fadeIn 0.15s ease-out',
+        'slide-up': 'slideUp 0.2s ease-out',
+        'scale-in': 'scaleIn 0.15s ease-out',
+      },
+      keyframes: {
+        fadeIn: {
+          '0%': { opacity: '0' },
+          '100%': { opacity: '1' },
+        },
+        slideUp: {
+          '0%': { opacity: '0', transform: 'translateY(8px)' },
+          '100%': { opacity: '1', transform: 'translateY(0)' },
+        },
+        scaleIn: {
+          '0%': { opacity: '0', transform: 'scale(0.96)' },
+          '100%': { opacity: '1', transform: 'scale(1)' },
         },
       },
     },