fix(android): require --device when several devices are connected

With no serial requested and more than one device online, pickDevice silently returned connected[0], but that serial is never threaded into the per-step adb calls, so every later bare adb command failed with "more than one device". Error instead and ask for --device, mirroring pickAVD; a single device stays unambiguous.

internal/android/android_test.go

@@ -47,13 +47,23 @@ func TestPickDevice_RequestedNotConnected(t *testing.T) {
 	}
 }
 
-func TestPickDevice_NoRequestUsesFirst(t *testing.T) {
-	serial, found, err := pickDevice("", []string{"emulator-5554", "physical-abc"})
+func TestPickDevice_NoRequestSingleDeviceUsesIt(t *testing.T) {
+	serial, found, err := pickDevice("", []string{"emulator-5554"})
 	if err != nil || !found || serial != "emulator-5554" {
 		t.Fatalf("got (%q, %v, %v), want (emulator-5554, true, nil)", serial, found, err)
 	}
 }
 
+func TestPickDevice_NoRequestMultipleDevicesErrors(t *testing.T) {
+	serial, found, err := pickDevice("", []string{"emulator-5554", "physical-abc"})
+	if err == nil {
+		t.Fatal("expected an error asking for --device when several devices are connected")
+	}
+	if found || serial != "" {
+		t.Fatalf("ambiguous selection must not pick a device, got (%q, %v)", serial, found)
+	}
+}
+
 func TestPickDevice_NoneConnectedFallsBackToAVD(t *testing.T) {
 	serial, found, err := pickDevice("", nil)
 	if err != nil || found || serial != "" {