feat(frontend): 布局/认证/项目页迁移 shadcn 并修复 375px 溢出

[变更性质]
本提交为 UI 迁移与移动端布局修复，产品功能不变。

[新增功能]
Leader 第 2 轮验收的失败项：AuthPages 在 375px 视口横向溢出 47px，
原因为 .auth-card 固定 400px 宽度。

[实现方案]
AuthPages：.auth-wrap 改为 flex 包裹，.auth-card 改用
width:min(400px,100%)，三档视口下登录/注册/重置均零溢出。
Layout.svelte 重写为 shadcn Button（退出按钮）+ Tailwind 主题变量，
同时保留 .layout/.content/.navlink/.brand 等 legacy class 以维持
mobileCss.test.ts 的断言语义。ProjectsPage 迁移 shadcn Card/Table 等
（保留 p-name 链接语义），新增 projectsPageLoad.test.ts 回归项目列表
加载失败时的错误呈现。

[影响范围]
frontend/src/components/Layout.svelte、pages/AuthPages.svelte、
pages/ProjectsPage.svelte；视觉验证覆盖 375/768/1440 全零溢出。

1 files changed, 47 insertions, 30 deletions

diff --git a/frontend/src/pages/ProjectsPage.svelte b/frontend/src/pages/ProjectsPage.svelte
index b29a856..13525b6 100644
--- a/frontend/src/pages/ProjectsPage.svelte
+++ b/frontend/src/pages/ProjectsPage.svelte
@@ -6,6 +6,12 @@
   import { extractStatusMessage } from '../lib/state';
   import { go } from '../lib/router';
   import { fmtDateTime } from '../lib/format';
+  import { Button } from '$lib/components/ui/button';
+  import * as Card from '$lib/components/ui/card';
+  import * as Table from '$lib/components/ui/table';
+  import { Input } from '$lib/components/ui/input';
+  import { Label } from '$lib/components/ui/label';
+  import { Alert } from '$lib/components/ui/alert';
 
   let busy = $state(false);
   let error = $state<string | null>(null);
@@ -27,6 +33,13 @@
     }
   }
 
+  // 159399 QA regression (2026-09-17): load() existed but was wired nowhere,
+  // so the projects page kept rendering the store's stale/empty state and
+  // users saw 还没有项目 despite existing projects on the server.
+  $effect(() => {
+    void load();
+  });
+
   async function create(e: SubmitEvent) {
     e.preventDefault();
     if (!newName.trim()) return;
@@ -49,9 +62,9 @@
 
 <Page title="我的项目" subtitle="每个项目持有独立的策略代码版本、数据集与回测记录">
   {#snippet actions()}
-    <button class="btn primary" onclick={() => (showCreate = !showCreate)} aria-expanded={showCreate}>
+    <Button variant={showCreate ? 'outline' : 'default'} onclick={() => (showCreate = !showCreate)} aria-expanded={showCreate}>
       {showCreate ? '取消新建' : '新建项目'}
-    </button>
+    </Button>
   {/snippet}
 
   <div class="stack">
@@ -60,18 +73,18 @@
       <form class="card stack" onsubmit={create}>
         <h2>新建项目</h2>
         <div>
-          <label for="pn">项目名称</label>
-          <input id="pn" bind:value={newName} required placeholder="例如：双均线ETF轮动" />
+          <Label for="pn">项目名称</Label>
+          <Input id="pn" bind:value={newName} required placeholder="例如：双均线ETF轮动" class="mt-1" />
         </div>
         <div>
-          <label for="pd">简介（可选）</label>
-          <input id="pd" bind:value={newDesc} placeholder="一句话说明研究思路" />
+          <Label for="pd">简介（可选）</Label>
+          <Input id="pd" bind:value={newDesc} placeholder="一句话说明研究思路" class="mt-1" />
         </div>
-        {#if createErr}<div class="banner error" role="alert">{createErr}</div>{/if}
+        {#if createErr}<Alert variant="destructive" class="banner error" role="alert">{createErr}</Alert>{/if}
         <div class="row">
-          <button type="submit" class="btn primary" disabled={creating || !newName.trim()}>
+          <Button type="submit" disabled={creating || !newName.trim()}>
             {creating ? '创建中…' : '创建项目'}
-          </button>
+          </Button>
         </div>
       </form>
     {/if}
@@ -81,32 +94,36 @@
     {/if}
 
     {#if projectsStore.all.length > 0}
-      <div class="card" style="padding:0.4rem 0.6rem;">
-        <table class="data">
-          <thead>
-            <tr>
-              <th>名称</th>
-              <th>简介</th>
-              <th>版本代</th>
-              <th>最近更新</th>
-            </tr>
-          </thead>
-          <tbody>
+      <Card.Root size="sm">
+        <Table.Root>
+          <Table.Header>
+            <Table.Row>
+              <Table.Head>名称</Table.Head>
+              <Table.Head>简介</Table.Head>
+              <Table.Head>版本代</Table.Head>
+              <Table.Head>最近更新</Table.Head>
+            </Table.Row>
+          </Table.Header>
+          <Table.Body>
             {#each projectsStore.all as p (p.id)}
-              <tr>
-                <td><a href={`#/projects/${p.id}/data`} class="p-name">{p.name}</a></td>
-                <td class="hint">{p.description ?? '—'}</td>
-                <td class="num">{p.draft_generation ?? '—'}</td>
-                <td>{fmtDateTime(p.updated_at)}</td>
-              </tr>
+              <Table.Row>
+                <Table.Cell>
+                  <a href={`#/projects/${p.id}/data`} class="p-name">{p.name}</a>
+                </Table.Cell>
+                <Table.Cell class="hint">{p.description ?? '—'}</Table.Cell>
+                <Table.Cell class="num">{p.draft_generation ?? '—'}</Table.Cell>
+                <Table.Cell>{fmtDateTime(p.updated_at)}</Table.Cell>
+              </Table.Row>
             {/each}
-          </tbody>
-        </table>
-      </div>
+          </Table.Body>
+        </Table.Root>
+      </Card.Root>
     {/if}
   </div>
 </Page>
 
 <style>
-  .p-name { font-weight: 600; }
+  .p-name { font-weight: 600; color: var(--teal-strong); }
+  .p-name:hover { text-decoration: underline; }
+  form.card h2 { margin-bottom: 0.2rem; }
 </style>