Fix internal API calls in Docker (use localhost instead of origin)

req.nextUrl.origin resolves to external domain behind a reverse proxy,
breaking server-to-server fetch calls. Use localhost:PORT instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/api/search/supplement/route.ts

@@ -12,7 +12,7 @@ export async function POST(req: NextRequest) {
     };
     const { query, region, targetCount, foundCount } = body;
 
-    const base = req.nextUrl.origin;
+    const base = `http://localhost:${process.env.PORT || 3000}`;
     const deficit = targetCount - foundCount;
 
     // 1. Try to generate an optimized query via GPT-4.1