fix: gofmt alignment in http3 server and surface errors in main.go demo

- gofmt the x509.Certificate struct literal in generateTLSConfig
- grpcSample() now checks and prints errors from http3.ServerRun and
  http3.ClientRun instead of silently discarding them (e.g. port
  conflicts previously failed with no output)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/grpc/http3/server.go

@@ -33,11 +33,11 @@ func generateTLSConfig() (*tls.Config, error) {
 		Subject: pkix.Name{
 			Organization: []string{"gRPC HTTP3 Canary"},
 		},
-		NotBefore: time.Now(),
-		NotAfter:  time.Now().Add(365 * 24 * time.Hour),
-		KeyUsage:  x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
+		NotBefore:   time.Now(),
+		NotAfter:    time.Now().Add(365 * 24 * time.Hour),
+		KeyUsage:    x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
 		ExtKeyUsage: []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
-		DNSNames:  []string{"localhost"},
+		DNSNames:    []string{"localhost"},
 		IPAddresses: []net.IP{net.ParseIP("127.0.0.1"), net.ParseIP("::1")},
 	}