fix(deploy): allow variable expansion in deploy scripts and add web health route

Fix heredoc quoting in deploy workflow to allow IMAGE_TAG and
REGISTRY_URL variable expansion. Add Next.js API health check route.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/app/api/health/route.ts

@@ -0,0 +1,9 @@
+import { NextResponse } from 'next/server';
+
+export function GET() {
+  return NextResponse.json({
+    status: 'ok',
+    service: 'goodgo-web',
+    timestamp: new Date().toISOString(),
+  });
+}