Add dynamic download redirect routes and update README links

landing/src/app/download/[platform]/route.ts

@@ -0,0 +1,42 @@
+import { type NextRequest, NextResponse } from 'next/server';
+import { getLatestRelease } from '@/lib/releases';
+
+export const dynamic = 'force-dynamic';
+
+const PLATFORM_MAP: Record<
+  string,
+  keyof Awaited<ReturnType<typeof getLatestRelease>>['downloadLinks']
+> = {
+  'mac-arm': 'macArm',
+  'mac-intel': 'macIntel',
+  windows: 'windows',
+  linux: 'linux',
+};
+
+export async function GET(
+  _request: NextRequest,
+  { params }: { params: Promise<{ platform: string }> },
+) {
+  const { platform } = await params;
+  const key = PLATFORM_MAP[platform];
+
+  if (!key) {
+    return NextResponse.json(
+      { error: `Unknown platform: ${platform}. Use: ${Object.keys(PLATFORM_MAP).join(', ')}` },
+      { status: 404 },
+    );
+  }
+
+  try {
+    const release = await getLatestRelease();
+    const url = release.downloadLinks[key];
+
+    if (!url) {
+      return NextResponse.json({ error: `No download available for ${platform}` }, { status: 404 });
+    }
+
+    return NextResponse.redirect(url);
+  } catch {
+    return NextResponse.redirect(`https://github.com/jamiepine/voicebox/releases/latest`);
+  }
+}