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_test.go

@@ -68,7 +68,7 @@ func TestDeviceRegistrationFlow(t *testing.T) {
 
 	// Step 3: Login as user to approve device
 	loginRequest := map[string]interface{}{
-		"login":    "testuser@example.com",
+		"login":    "testuser@tests.bookhoard.internal",
 		"password": "Test@Pass123!",
 	}
 	loginBody, _ := json.Marshal(loginRequest)