feat: 重构主题管理并优化UI样式

重构主题管理逻辑，将useTheme composable迁移至pinia store中管理
更新页面布局和样式，调整边距和卡片样式
添加新的主题配置文件并移除旧的主题图片资源
优化登录页和设置页的UI交互
更新unocss配置添加更多flex快捷类

fastapp/src/static/images/login-bg-bak.svg

@@ -1,31 +0,0 @@
-<svg width="100%" height="100%" viewBox="0 0 1000 1000" xmlns="http://www.w3.org/2000/svg">
-  <!-- 背景渐变 -->
-  <defs>
-    <linearGradient id="bgGradient" x1="0%" y1="0%" x2="100%" y2="100%">
-      <stop offset="0%" stop-color="#94BFFF" />
-      <stop offset="100%" stop-color="#165DFF" />
-    </linearGradient>
-    
-    <!-- 图形渐变 -->
-    <linearGradient id="shapeGradient" x1="0%" y1="0%" x2="100%" y2="100%">
-      <stop offset="0%" stop-color="#ffffff" stop-opacity="0.3" />
-      <stop offset="100%" stop-color="#ffffff" stop-opacity="0.15" />
-    </linearGradient>
-  </defs>
-  
-  <!-- 透明背景，不完全填充 -->
-  <rect width="100%" height="50%" fill="url(#bgGradient)" />
-  
-  <!-- 左侧方块装饰 -->
-  <rect x="100" y="150" width="120" height="120" rx="15" fill="url(#shapeGradient)" transform="rotate(-10, 160, 210)" opacity="0.7" />
-  <rect x="190" y="90" width="80" height="80" rx="10" fill="url(#shapeGradient)" transform="rotate(15, 230, 130)" opacity="0.6" />
-  <rect x="60" y="250" width="100" height="100" rx="10" fill="url(#shapeGradient)" transform="rotate(-5, 110, 300)" opacity="0.5" />
-  
-  <!-- 右侧圆形装饰 -->
-  <circle cx="750" cy="150" r="60" fill="url(#shapeGradient)" opacity="0.7" />
-  <circle cx="820" cy="230" r="90" fill="url(#shapeGradient)" opacity="0.5" />
-  <circle cx="690" cy="250" r="40" fill="url(#shapeGradient)" opacity="0.6" />
-  
-  <!-- 底部波浪 -->
-  <path d="M0,900 C200,800 350,950 550,870 C750,790 850,900 1000,850 L1000,1000 L0,1000 Z" fill="#ffffff" />
-</svg>