fix(github-oauth): use NEXTAUTH_URL for redirect_uri instead of req.url.origin

Behind Coolify's proxy, req.url resolves to 0.0.0.0:3000 which GitHub
rejects as an unregistered redirect URI. Prefer NEXTAUTH_URL env var.

Made-with: Cursor

app/api/integrations/github/connect/route.ts

@@ -33,7 +33,11 @@ export async function GET(req: Request) {
   }
 
   const url = new URL(req.url);
-  const callbackUrl = `${url.origin}/api/integrations/github/callback`;
+  // Use NEXTAUTH_URL when available — behind a proxy req.url.origin
+  // resolves to the internal bind address (0.0.0.0) rather than the
+  // public hostname, which GitHub then rejects as an unregistered URI.
+  const appOrigin = (process.env.NEXTAUTH_URL ?? url.origin).replace(/\/$/, "");
+  const callbackUrl = `${appOrigin}/api/integrations/github/callback`;
   const returnTo = url.searchParams.get("returnTo") ?? "/";
 
   const state = randomBytes(16).toString("hex");