added some tests? and CI

backend/src/main/java/dev/ksan/etfoglasiserver/service/DeviceTokenService.java

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+package dev.ksan.etfoglasiserver.service;
+
+public class DeviceTokenService {
+}

backend/src/test/java/dev/ksan/etfoglasiserver/controller/DeviceTokenControllerTest.java

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+package dev.ksan.etfoglasiserver.controller;
+
+public class DeviceTokenControllerTest {
+}

backend/src/test/java/dev/ksan/etfoglasiserver/controller/UserControllerIntegrationTest.java

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+package dev.ksan.etfoglasiserver.controller;
+
+public class UserControllerIntegrationTest {
+}

backend/src/test/java/dev/ksan/etfoglasiserver/service/NotificationServiceTest.java

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+package dev.ksan.etfoglasiserver.service;
+
+public class NotificationServiceTest {
+}