test: update test files to use @tests.bookhoard.internal domain

Update email domain in remaining test files:
- device_cap_test.go
- device_test.go
- queue_test.go
- refresh_token_test.go
- seven_day_session_test.go

All test files now consistently use the dedicated test domain
to prevent conflicts with real user data.

cmd/server/tests/device_cap_test.go

@@ -411,7 +411,7 @@ func createTestUserForMaxDevices(t *testing.T, ts *httptest.Server, adminToken s
 func getAdminToken(t *testing.T, ts *httptest.Server, userID uuid.UUID) string {
 	// First, try to login as the admin user (testuser who was created with admin role)
 	loginPayload := map[string]interface{}{
-		"login":    "testuser@example.com",
+		"login":    "testuser@tests.bookhoard.internal",
 		"password": "Test@Pass123!",
 	}