feat: initial Greasy Sprocket website — Astro static + Go feedback service

- Astro 5.x static site with content collections for extensions
- Pages: index, [slug] (per-extension), coffee (Ko-fi), feedback form
- Go binary gs-feedback: SQLite storage + Discord webhook notification
- Nginx config: static serving + POST proxy to Go backend
- Deploy script: build + rsync to VPS
- ThockBoard landing page with features and sound pack listing

astro/src/pages/[slug].astro

@@ -0,0 +1,59 @@
+---
+import Base from '../layouts/Base.astro';
+import { getCollection } from 'astro:content';
+
+export async function getStaticPaths() {
+  const extensions = await getCollection('extensions');
+  return extensions.map((ext) => ({
+    params: { slug: ext.slug },
+    props: { ext },
+  }));
+}
+
+const { ext } = Astro.props;
+const { Content } = await ext.render();
+---
+
+<Base title={`${ext.data.name} — Greasy Sprocket`} description={ext.data.tagline}>
+  <section class="ext-hero">
+    <div class="container">
+      <div class="info">
+        <span class="badge">100% Free</span>
+        <h1>{ext.data.name}</h1>
+        <p>{ext.data.tagline}</p>
+        <div style="display:flex;gap:12px">
+          {ext.data.chromeStoreUrl && (
+            <a href={ext.data.chromeStoreUrl} class="btn btn-primary" target="_blank" rel="noopener">
+              Add to Chrome
+            </a>
+          )}
+          {ext.data.downloadUrl && (
+            <a href={ext.data.downloadUrl} class="btn btn-outline">
+              Download ZIP
+            </a>
+          )}
+        </div>
+      </div>
+      {ext.data.screenshot && (
+        <div class="screenshot">
+          <img src={ext.data.screenshot} alt={`${ext.data.name} screenshot`} />
+        </div>
+      )}
+    </div>
+  </section>
+
+  <section class="section">
+    <div class="container">
+      <div class="feature-list">
+        {ext.data.features?.map((feature: string) => (
+          <div class="feature-item">
+            <h4>✅ {feature}</h4>
+          </div>
+        ))}
+      </div>
+      <div style="margin-top:32px">
+        <Content />
+      </div>
+    </div>
+  </section>
+</Base>