fix: 功能展示风格提到第一位+比例优化 — 右侧400px更紧凑，左侧间距缩减，默认登录页改为sidepanel

frontend/src/pages/AppearanceSettings.tsx

@@ -193,7 +193,7 @@ export default function AppearanceSettings() {
                           </div>
                         </div>
                         {/* Right: login form */}
-                        <div className="w-[35%] p-1 flex flex-col justify-center gap-0.5" style={{ background: 'var(--dg-bg-secondary, rgba(255,255,255,0.03))' }}>
+                        <div className="w-[30%] p-1 flex flex-col justify-center gap-0.5" style={{ background: 'var(--dg-bg-secondary, rgba(255,255,255,0.03))' }}>
                           <div className="w-3 h-0.5 rounded-sm" style={{ background: 'rgba(255,255,255,0.3)' }} />
                           <div className="w-full h-0.5 rounded-sm" style={{ background: 'var(--dg-bg-tertiary, rgba(255,255,255,0.08))' }} />
                           <div className="w-full h-0.5 rounded-sm" style={{ background: 'var(--dg-bg-tertiary, rgba(255,255,255,0.08))' }} />