fix: 修复浅色模式下 text-white 文字不可见，新增主题安全色规范

极速救场标题、个人中心导航和输入框改用语义色

src/app/profile/page.tsx

@@ -260,7 +260,7 @@ export default function ProfilePage() {
       <div className="h-dvh bg-background pb-16 overflow-y-auto scrollbar-none">
         <nav className="sticky top-0 z-10 flex h-14 items-center gap-3 bg-background/80 px-4 backdrop-blur-sm">
           <div className="h-8 w-8" />
-          <h1 className="flex-1 text-base font-bold text-white">个人中心</h1>
+          <h1 className="flex-1 text-base font-bold text-heading">个人中心</h1>
         </nav>
         <div className="mx-auto max-w-sm px-5">
           <ProfileCardSkeleton />
@@ -297,7 +297,7 @@ export default function ProfilePage() {
         >
           <ArrowLeft size={20} />
         </button>
-        <h1 className="flex-1 text-base font-bold text-white">个人中心</h1>
+        <h1 className="flex-1 text-base font-bold text-heading">个人中心</h1>
       </nav>
 
       <div className="mx-auto max-w-sm px-5">
@@ -329,7 +329,7 @@ export default function ProfilePage() {
                     }}
                     maxLength={16}
                     autoFocus
-                    className="h-8 flex-1 rounded-lg border-none bg-elevated px-2 text-sm text-white outline-none ring-1 ring-border focus:ring-2 focus:ring-accent/50"
+                    className="h-8 flex-1 rounded-lg border-none bg-elevated px-2 text-sm text-foreground outline-none ring-1 ring-border focus:ring-2 focus:ring-accent/50"
                   />
                   <button
                     onClick={handleSaveUsername}