feat(layout): 基础布局/导航/页脚/明暗不闪烁

- BaseLayout：字体三轨统持、viewport-fit=cover、theme-color 双套、skip-link
- Header：≤4 项导航纪律 + sticky 毛玻璃 + aria-current；搜索 icon 占位待 T8
- Footer：ICP 备案链接（法定保留）+ built-from 具名槽位待 T7
- ThemeScript：head 内联先于首帧，手选 > 系统偏好，防白闪

验证: pnpm astro build exit 0；dist/index.html 含 ICP 文案与跳到正文链

Spec: 2026-10-24_add-blog-skeleton
Co-authored-by: GLM-5.3

src/components/Header.astro

@@ -0,0 +1,84 @@
+---
+// 顶部导航：≤4 项纪律（防 higan 十项复发）；当前页 aria-current
+const nav = [
+  { href: '/archives/', label: '文章' },
+  { href: '/gallery/', label: '图库' },
+  { href: '/about/', label: '关于' },
+];
+const path = Astro.url.pathname;
+const isCurrent = (href: string) =>
+  path === href || path === href.replace(/\/$/, '') || path.startsWith(href);
+---
+
+<header class="site-header safe-area">
+  <div class="container-wide header-inner">
+    <a href="/" class="brand" aria-label="wait4x 首页">wait4x</a>
+    <nav aria-label="主导航">
+      <ul>
+        {nav.map((item) => (
+          <li>
+            <a
+              href={item.href}
+              class="tap nav-link"
+              aria-current={isCurrent(item.href) ? 'page' : undefined}
+            >
+              {item.label}
+            </a>
+          </li>
+        ))}
+        <!-- 搜索入口：T8 Pagefind 面板接管，先留可聚焦占位 -->
+        <li>
+          <button class="tap nav-link" type="button" data-search-trigger aria-label="搜索">
+            <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" aria-hidden="true">
+              <circle cx="11" cy="11" r="7"></circle>
+              <path d="m20 20-3.5-3.5"></path>
+            </svg>
+          </button>
+        </li>
+      </ul>
+    </nav>
+  </div>
+</header>
+
+<style>
+  .site-header {
+    border-bottom: 1px solid var(--line);
+    position: sticky;
+    top: 0;
+    background: color-mix(in oklab, var(--bg) 88%, transparent);
+    backdrop-filter: blur(8px);
+    z-index: 10;
+  }
+  .header-inner {
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    height: 56px;
+  }
+  .brand {
+    font-family: var(--font-mono);
+    font-weight: 700;
+    font-size: 18px;
+    color: var(--ink-1);
+    letter-spacing: 0.02em;
+  }
+  nav ul {
+    display: flex;
+    gap: var(--space-2);
+    list-style: none;
+    padding: 0;
+    margin: 0;
+  }
+  .nav-link {
+    font-size: 15px;
+    color: var(--ink-3);
+    padding-inline: var(--space-2);
+    border-radius: 6px;
+    transition: color var(--dur) var(--ease);
+  }
+  .nav-link:hover { color: var(--ink-1); }
+  .nav-link[aria-current='page'] { color: var(--accent); }
+  @media (max-width: 560px) {
+    .nav-link { font-size: 14px; padding-inline: var(--space-1); }
+  }
+</style>