feat: 10个登录页图标统一 — 蓝紫渐变(#3b82f6→#8b5cf6)+白色盾牌勾选，与favicon一致

frontend/src/components/login/NeonCityView.tsx

@@ -268,7 +268,7 @@ export default function NeonCityView(): JSX.Element {
                 width: 44,
                 height: 44,
                 borderRadius: 12,
-                background: 'linear-gradient(135deg, #ec4899, #06b6d4)',
+                background: 'linear-gradient(135deg, #3b82f6, #8b5cf6)',
                 display: 'inline-flex',
                 alignItems: 'center',
                 justifyContent: 'center',
@@ -276,20 +276,7 @@ export default function NeonCityView(): JSX.Element {
                 boxShadow: '0 0 15px rgba(236, 72, 153, 0.5), 0 0 30px rgba(6, 182, 212, 0.3)',
               }}
             >
-              <svg
-                width="22"
-                height="22"
-                viewBox="0 0 24 24"
-                fill="none"
-                stroke="#fff"
-                strokeWidth="2"
-                strokeLinecap="round"
-                strokeLinejoin="round"
-              >
-                <ellipse cx="12" cy="5" rx="9" ry="3" />
-                <path d="M21 12c0 1.66-4 3-9 3s-9-1.34-9-3" />
-                <path d="M3 5v14c0 1.66 4 3 9 3s9-1.34 9-3V5" />
-              </svg>
+              <svg width="22" height="22" viewBox="0 0 24 24" fill="none" stroke="#fff" strokeWidth="1.5" strokeLinecap="round" strokeLinejoin="round"><path d="M12 2L20 6V11C20 16 16 19.5 12 22C8 19.5 4 16 4 11V6L12 2Z" /><path d="M9 12L11 14L15 10" /></svg>
             </div>
 
             {/* Title */}
@@ -464,20 +451,7 @@ export default function NeonCityView(): JSX.Element {
             >
               {loading ? (
                 <span style={{ display: 'inline-flex', alignItems: 'center', gap: 8 }}>
-                  <svg
-                    width="16"
-                    height="16"
-                    viewBox="0 0 24 24"
-                    fill="none"
-                    stroke="currentColor"
-                    strokeWidth="2"
-                    strokeLinecap="round"
-                    strokeLinejoin="round"
-                    style={{ animation: 'spin 1s linear infinite' }}
-                  >
-                    <style>{`@keyframes spin { to { transform: rotate(360deg); } }`}</style>
-                    <path d="M21 12a9 9 0 1 1-6.219-8.56" />
-                  </svg>
+                  <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="#fff" strokeWidth="1.5" strokeLinecap="round" strokeLinejoin="round"><path d="M12 2L20 6V11C20 16 16 19.5 12 22C8 19.5 4 16 4 11V6L12 2Z" /><path d="M9 12L11 14L15 10" /></svg>
                   登录中...
                 </span>
               ) : (