feat: build index page with sorted post listing and ArticleCard components

This replaces the smoke test index with a real page that:
- Imports getCollection, BaseLayout, NavBar, ArticleCard, getReadingTime
- Fetches all posts and sorts descending by date
- Maps posts to ArticleCard components with title, date, type, summary, slug, readingTime
- Styles .post-list with prose max-width, space-6/space-12 margins, flex column, space-2 gap

Generated with [Amplifier](https://github.com/microsoft/amplifier)

Co-Authored-By: Amplifier <240397093+microsoft-amplifier@users.noreply.github.com>

src/pages/index.astro

@@ -1,28 +1,39 @@
 ---
+import { getCollection } from 'astro:content';
 import BaseLayout from '../layouts/BaseLayout.astro';
 import NavBar from '../components/NavBar.astro';
-import PostHeader from '../components/PostHeader.astro';
+import ArticleCard from '../components/ArticleCard.astro';
+import { getReadingTime } from '../utils/reading-time';
+
+const posts = await getCollection('posts');
+const sortedPosts = posts.sort((a, b) => b.data.date.getTime() - a.data.date.getTime());
 ---
 
-<BaseLayout title="Crash Test Dev" description="Foundation smoke test">
+<BaseLayout title='Crash Test Dev'>
   <NavBar slot="nav" />
-  <PostHeader
-    title="Speeding Up Webpack Typescript Incremental Builds by 7x"
-    date={new Date('2019-08-16')}
-    type="post"
-    readingTime={12}
-  />
-  <div style="max-width: var(--width-prose); margin-left: auto; margin-right: auto; display: flex; flex-direction: column; gap: var(--space-4);">
-    <p style="font-family: var(--font-prose); font-size: 18px; color: var(--text-primary); line-height: var(--leading-prose);">
-      This is the prose voice — Source Serif 4 at 18px. It carries the reader through long-form
-      content with a warm, readable serif that feels like ink on parchment.
-    </p>
-    <p style="font-family: var(--font-structure); font-size: 14px; color: var(--text-secondary); line-height: var(--leading-normal);">
-      This is the structure voice — Inter at 14px in secondary color. It handles navigation,
-      labels, metadata, and UI chrome with a clean sans-serif that stays out of the way.
-    </p>
-    <code style="display: block; font-family: var(--font-evidence); font-size: var(--type-sm); color: var(--code-text); background: var(--surface-code); padding: var(--space-2); border-radius: var(--rounded-md); border-left: 3px solid var(--accent-primary);">
-      const buildTime = 7 * previousBuildTime; // evidence voice — JetBrains Mono
-    </code>
-  </div>
+  <section class="post-list" aria-label="All posts">
+    {sortedPosts.map((post) => (
+      <ArticleCard
+        title={post.data.title}
+        date={post.data.date}
+        type={post.data.type}
+        summary={post.data.summary}
+        slug={post.id}
+        readingTime={post.body ? getReadingTime(post.body) : undefined}
+      />
+    ))}
+  </section>
 </BaseLayout>
+
+<style>
+  .post-list {
+    max-width: var(--width-prose);
+    margin-top: var(--space-6);
+    margin-bottom: var(--space-12);
+    margin-left: auto;
+    margin-right: auto;
+    display: flex;
+    flex-direction: column;
+    gap: var(--space-2);
+  }
+</style>