feat: 品牌重命名 SQL-Platform → OpsxSQL — 12个文件18处替换，覆盖所有登录组件+Layout+index.html

frontend/src/components/Layout.tsx

@@ -61,7 +61,7 @@ export default function Layout() {
               <Shield className="w-4 h-4 text-white" />
             </div>
             <span className="text-base font-bold dg-gradient-text whitespace-nowrap">
-              SQL-Platform
+              OpsxSQL
             </span>
           </div>
         </div>
@@ -127,7 +127,7 @@ export default function Layout() {
         <header className="h-14 bg-[var(--dg-bg-secondary)] border-b border-[var(--dg-border)] flex items-center justify-between px-5 flex-shrink-0">
           {/* Breadcrumb area */}
           <div className="flex items-center gap-1.5 text-sm">
-            <span className="text-[var(--dg-text-muted)] font-medium">SQL-Platform</span>
+            <span className="text-[var(--dg-text-muted)] font-medium">OpsxSQL</span>
             {breadcrumbInfo.sectionLabel && (
               <>
                 <ChevronRight className="w-3.5 h-3.5 text-[var(--dg-text-muted)] opacity-50" />