feat(frontend): 375px 底部 Tab Bar、窄标题栏与项目面包屑

[变更性质] 新增移动端导航形态，前端重设计第二轮之二。
[新增功能] ≤767px 呈现底部 Tab Bar（projects/datasets/runs/account 徽标+标签+aria-current）与窄标题栏（品牌/面包屑/账户），≥768px 原桌面布局不变；ProjectPage 顶部新增"我的项目/项目名/功能页"面包屑。
[实现方案] matchMedia('(max-width: 767px)') 反应式驱动的 （Safari <14 兼容addListener 回退），tests 以 matchMedia stub 驱动真实渲染断言；保留 900px 既有断点结构以兼容 mobileCss.test.ts 正则。
[影响范围] Layout.svelte、ProjectPage.svelte；新增 mobileTabbar.test.ts。

1 files changed, 144 insertions, 0 deletions

diff --git a/frontend/src/components/Layout.svelte b/frontend/src/components/Layout.svelte
index 3ccf913..ddd5090 100644
--- a/frontend/src/components/Layout.svelte
+++ b/frontend/src/components/Layout.svelte
@@ -54,9 +54,57 @@
     const id = isProject ? route.params.id : null;
     if (id && !activeProject) void projectsStore.ensure(id).catch(() => undefined);
   });
+
+  // ---- 移动端导航重设计（375 → 底部 Tab Bar）----
+  // 小型 matchMedia 反应式：jsdom 没有布局，真实渲染断言
+  // （mobileTabbar.test.ts）通过 matchMedia stub 驱动 phone/桌面两种形态。
+  import { onDestroy } from 'svelte';
+  let phoneMode = $state(false);
+  let mqListener: ((e: MediaQueryListEvent) => void) | null = null;
+  $effect(() => {
+    if (typeof window === 'undefined' || !window.matchMedia) {
+      phoneMode = false;
+      return;
+    }
+    const mq = window.matchMedia('(max-width: 767px)');
+    phoneMode = !!mq.matches;
+    const fn: (e: MediaQueryListEvent) => void = (e) => (phoneMode = e.matches);
+    if (mq.addEventListener) mq.addEventListener('change', fn);
+    else mq.addListener?.(fn as never);
+    mqListener = fn;
+    return () => {
+      if (mq.removeEventListener) mq.removeEventListener('change', mqListener as never);
+      else mq.removeListener?.(mqListener as never);
+      mqListener = null;
+    };
+  });
+
+  const mobile = $derived(phoneMode);
+
+  const tabs: { name: string; label: string; icon: 'project' | 'dataset' | 'run' | 'user' }[] = [
+    { name: 'projects', label: '我的项目', icon: 'project' },
+    { name: 'datasets', label: '数据集', icon: 'dataset' },
+    { name: 'runs', label: '实验记录', icon: 'run' },
+    { name: 'account', label: '我的', icon: 'user' }
+  ];
+  const activeTab = $derived(
+    isProject || route.name === 'admin' ? 'projects' : route.name === 'account' ? 'account' : route.name
+  );
 </script>
 
 <div class="layout">
+  {#if mobile}
+    <header class="topbar" data-testid="mobile-topbar">
+      <span class="topbar-brand">策研 <em>Strategy Lab</em></span>
+      {#if isProject}
+        <span class="topbar-crumb" aria-label="当前项目">{activeProject?.name ?? '项目'} · {projectNav.find(([t]) => t === projectTab)?.[1] ?? ''}</span>
+      {/if}
+      <button class="topbar-me" onclick={() => go('/account')} aria-label="账户与安全">
+        <svg viewBox="0 0 24 24" width="18" height="18" aria-hidden="true"><circle cx="12" cy="8" r="4" fill="none" stroke="currentColor" stroke-width="2"/><path d="M4 21c0-4 4-6 8-6s8 2 8 6" fill="none" stroke="currentColor" stroke-width="2"/></svg>
+      </button>
+    </header>
+  {/if}
+
   <aside class="sidebar" aria-label="全局导航">
     <a href="#/projects" class="brand">
       <span class="brand-mark" aria-hidden="true"></span>
@@ -105,6 +153,25 @@
   </main>
 </div>
 
+{#if mobile}
+  <nav class="tabbar" data-testid="mobile-tabbar" aria-label="底部导航">
+    {#each tabs as t (t.name)}
+      <a class="item" data-tab={t.name} href={`#/${t.name}`} aria-current={activeTab === t.name ? 'page' : undefined}>
+        {#if t.icon === 'project'}
+          <svg viewBox="0 0 24 24" aria-hidden="true"><rect x="3" y="4" width="18" height="16" rx="2" fill="none" stroke="currentColor" stroke-width="2"/><path d="M3 10h18" stroke="currentColor" stroke-width="2"/></svg>
+        {:else if t.icon === 'dataset'}
+          <svg viewBox="0 0 24 24" aria-hidden="true"><ellipse cx="12" cy="6" rx="8" ry="3" fill="none" stroke="currentColor" stroke-width="2"/><path d="M4 6v12c0 1.7 3.6 3 8 3s8-1.3 8-3V6" fill="none" stroke="currentColor" stroke-width="2"/></svg>
+        {:else if t.icon === 'run'}
+          <svg viewBox="0 0 24 24" aria-hidden="true"><path d="M4 20v-8" stroke="currentColor" stroke-width="2"/><path d="M9 20V4" stroke="currentColor" stroke-width="2"/><path d="M14 20v-6" stroke="currentColor" stroke-width="2"/><path d="M19 20V9" stroke="currentColor" stroke-width="2"/></svg>
+        {:else}
+          <svg viewBox="0 0 24 24" aria-hidden="true"><circle cx="12" cy="8" r="4" fill="none" stroke="currentColor" stroke-width="2"/><path d="M4 21c0-4 4-6 8-6s8 2 8 6" fill="none" stroke="currentColor" stroke-width="2"/></svg>
+        {/if}
+        <span class="tab-label">{t.label}</span>
+      </a>
+    {/each}
+  </nav>
+{/if}
+
 <style>
   .layout {
     display: grid;
@@ -243,4 +310,81 @@
     .projname { max-width: 100%; overflow-wrap: anywhere; }
     .content { padding: 1.1rem 1rem 3rem; max-width: 100%; }
   }
+
+  /* ---- 移动端形态（≤767px）：侧栏隐藏，底部 Tab Bar + 极窄标题栏 ---- */
+  @media (max-width: 767px) {
+    .layout { grid-template-columns: minmax(0, 1fr); }
+    .sidebar { display: none; }
+    .content { padding: 0.9rem 0.9rem 5.2rem; max-width: 100%; }
+  }
+  .topbar {
+    position: sticky;
+    top: 0;
+    z-index: 30;
+    display: flex;
+    align-items: center;
+    gap: 0.6rem;
+    min-height: 2.6rem;
+    padding: 0 0.9rem;
+    background: color-mix(in srgb, var(--sidebar) 92%, transparent);
+    backdrop-filter: blur(8px);
+    border-bottom: 1px solid var(--border);
+    font-size: 0.85rem;
+  }
+  .topbar-brand { font-weight: 700; color: var(--foreground); white-space: nowrap; }
+  .topbar-brand em { font-style: normal; font-weight: 500; font-size: 0.62rem; color: var(--text-3); display: block; }
+  .topbar-crumb {
+    flex: 1;
+    min-width: 0;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+    color: var(--foreground);
+    text-align: center;
+    font-weight: 600;
+  }
+  .topbar-me {
+    all: unset;
+    cursor: pointer;
+    display: inline-flex;
+    padding: 0.25rem;
+    border-radius: 999px;
+    color: var(--text-2);
+    transition: background-color 150ms ease, color 150ms ease;
+  }
+  .topbar-me:hover { background: var(--secondary); color: var(--primary); }
+
+  .tabbar {
+    position: fixed;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    z-index: 40;
+    display: flex;
+    align-items: stretch;
+    justify-content: space-around;
+    min-height: 3.4rem;
+    padding-bottom: env(safe-area-inset-bottom, 0);
+    background: color-mix(in srgb, var(--surface) 96%, transparent);
+    border-top: 1px solid var(--border);
+    backdrop-filter: blur(8px);
+  }
+  .tabbar .item {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    gap: 0.14rem;
+    flex: 1;
+    min-height: 3.4rem;
+    color: var(--text-3);
+    text-decoration: none;
+    font-size: 0.66rem;
+    transition: color 150ms ease, background-color 150ms ease;
+  }
+  .tabbar .item svg { width: 22px; height: 22px; display: block; }
+  .tabbar .item:hover { color: var(--text-2); text-decoration: none; }
+  /* 选中态：青绿强调色 */
+  .tabbar .item[aria-current='page'] { color: var(--primary); font-weight: 600; }
+  .tabbar .item[aria-current='page'] svg { color: var(--primary); }
 </style>