fix: FCM 서비스 계정 파일을 classpath에서 로드하도록 수정

backend/src/main/java/com/eatall/backend/config/firebase/FcmConfig.java

@@ -7,6 +7,7 @@
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.io.ClassPathResource;
 
 import java.io.InputStream;
 import java.nio.file.Files;
@@ -26,13 +27,11 @@ public void initialize() {
                 return;
             }
 
-            Path path = Path.of(keyPath);
-            if (!Files.exists(path)) {
-                log.warn("FCM service account key file not found at: {}", keyPath);
-                return;
-            }
+            try (InputStream serviceAccount = getServiceAccountInputStream()) {
+                if (serviceAccount == null) {
+                    return;
+                }
 
-            try (InputStream serviceAccount = Files.newInputStream(path)) {
                 FirebaseOptions options = FirebaseOptions.builder()
                         .setCredentials(GoogleCredentials.fromStream(serviceAccount))
                         .build();
@@ -46,4 +45,23 @@ public void initialize() {
             log.error("FCM initialization failed", e);
         }
     }
+
+    private InputStream getServiceAccountInputStream() throws Exception {
+        if (keyPath.startsWith("classpath:")) {
+            String resourcePath = keyPath.substring("classpath:".length());
+            ClassPathResource resource = new ClassPathResource(resourcePath);
+            if (!resource.exists()) {
+                log.warn("FCM service account resource not found in classpath: {}", keyPath);
+                return null;
+            }
+            return resource.getInputStream();
+        }
+
+        Path path = Path.of(keyPath);
+        if (!Files.exists(path)) {
+            log.warn("FCM service account key file not found at: {}", keyPath);
+            return null;
+        }
+        return Files.newInputStream(path);
+    }
 }