修复移动端顶栏折行与头像裁剪弹窗被底部主菜单遮挡

- 主站顶栏在所有断点保持单行：去掉顶栏与动作区的 flex-wrap，品牌和下载、泥点、账户入口不再折成两行
- 窄屏（<640px）下载入口收起为 44×44 图标按钮，保留 aria-label/title，≥640px 恢复「下载客户端」完整文案
- 窄屏（<480px）顶栏品牌只保留 IP 标识，让出空间给下载、泥点与账户入口，并收紧窄屏动作区间距
- 头像裁剪弹窗去掉 portal={false}，改由 UnifiedModal 默认 portal 渲染到 document.body
- 个人中心两级弹窗壳层同步去掉 portal={false}，昵称等个人中心弹窗一并回到页面级层级
- 弹窗不再受 .platform-desktop-layout 的 z-index:1 stacking context 限制，层级高于固定底部主菜单（z-index:60）
- 共享记忆补记单行顶栏口径与「内联弹窗被固定底栏压住」的排障经验

src/components/common/SquareImageCropModal.tsx

@@ -319,7 +319,6 @@ export function SquareImageCropModal({
       closeLabel={labels.close}
       closeVariant="profileCompact"
       closeIcon="×"
-      portal={false}
       zIndexClassName="z-[80]"
       panelClassName="platform-remap-surface max-w-sm rounded-[1.4rem]"
       headerClassName="border-white/10 px-5 py-4"

src/components/creation-home/ClientDownloadEntry.tsx

@@ -75,14 +75,16 @@ export function ClientDownloadEntry() {
         tone="secondary"
         size="sm"
         shape="pill"
-        className="min-h-11 shrink-0 whitespace-nowrap"
+        aria-label="下载客户端"
+        title="下载客户端"
+        className="min-h-11 shrink-0 gap-0 whitespace-nowrap max-sm:h-11 max-sm:w-11 max-sm:px-0 sm:gap-2 sm:px-4"
         onClick={() => {
           setState({ status: 'loading' });
           setOpen(true);
         }}
       >
-        <Download className="h-4 w-4" aria-hidden="true" />
-        下载客户端
+        <Download className="h-4 w-4 shrink-0" aria-hidden="true" />
+        <span className="hidden sm:inline">下载客户端</span>
       </PlatformActionButton>
       <UnifiedModal
         open={open}

src/components/platform-entry/PlatformEntryActiveFlowShell.tsx

@@ -618,8 +618,8 @@ export function PlatformEntryFlowShellImpl({
             </aside>
 
             <div className="platform-desktop-main flex min-w-0 flex-1 flex-col">
-              <header className="platform-desktop-topbar flex min-h-16 shrink-0 flex-wrap items-center justify-between gap-1 gap-y-2 px-4 py-2 sm:flex-nowrap sm:gap-3 sm:px-6 sm:py-0">
-                <div className="min-w-0 shrink-0 lg:hidden">
+              <header className="platform-desktop-topbar flex min-h-16 shrink-0 flex-nowrap items-center justify-between gap-1 px-4 py-2 sm:gap-3 sm:px-6 sm:py-0">
+                <div className="platform-desktop-topbar__brand min-w-0 shrink-0 lg:hidden">
                   <ActivePlatformBrand />
                 </div>
                 <div className="platform-desktop-topbar__brand-search hidden min-w-0 flex-1 items-center lg:flex">
@@ -662,7 +662,7 @@ export function PlatformEntryFlowShellImpl({
                   </form>
                 </div>
 
-                <div className="platform-desktop-topbar__actions flex max-w-full shrink-0 flex-wrap items-center gap-1 sm:flex-nowrap sm:gap-2 lg:gap-3">
+                <div className="platform-desktop-topbar__actions flex min-w-0 shrink-0 items-center gap-1 sm:gap-2 lg:gap-3">
                   <ClientDownloadEntry />
                   {isAuthenticated ? (
                     <PlatformMudPointWalletEntry

src/components/platform-entry/PlatformProfileModalShell.tsx

@@ -84,7 +84,6 @@ export function PlatformProfileModalShell({
       showCloseButton={showCloseButton}
       closeOnBackdrop={false}
       closeOnEscape={false}
-      portal={false}
       size={size}
       zIndexClassName={zIndexClassName}
       overlayClassName={PROFILE_MODAL_OVERLAY_CLASS}
@@ -128,7 +127,6 @@ export function PlatformProfileSecondaryModalShell({
       showCloseButton={false}
       closeOnBackdrop={false}
       closeOnEscape={false}
-      portal={false}
       size={size}
       zIndexClassName={zIndexClassName}
       overlayClassName={

src/index.css

@@ -12626,6 +12626,22 @@ button.image-canvas-editor__reference-chip:disabled {
     min-width: 0;
     padding-inline: 0.12rem;
   }
+
+  .platform-desktop-shell--workbench
+    .platform-desktop-topbar
+    .platform-desktop-topbar__actions {
+    gap: 0.38rem !important;
+  }
+}
+
+/* 窄屏顶栏必须保持单行：品牌只保留 IP 标识，字标让位给下载、泥点与账户入口。 */
+@media (max-width: 479px) {
+  .platform-desktop-shell--workbench
+    .platform-desktop-topbar
+    .platform-desktop-topbar__brand
+    .platform-brand-logo__copy {
+    display: none;
+  }
 }
 
 .platform-desktop-shell--workbench .platform-desktop-rail {