feat(version): answer the build commit and time

GET /api/version is public. CI passes GIT_SHA and BUILD_TIME as Docker build args; a local build answers dev.

src/test/java/auth_service/configuration/security/PublicEndpointsTest.java

@@ -42,4 +42,11 @@ class PublicEndpointsTest extends AbstractIntegrationTest {
         int status = mockMvc.perform(get("/actuator/prometheus")).andReturn().getResponse().getStatus();
         assertTrue(Set.of(401, 403).contains(status), "/actuator/prometheus answered " + status);
     }
+
+    @Test
+    void versionIsPublic() throws Exception {
+        mockMvc.perform(get("/api/version"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.commit").isString());
+    }
 }

src/test/java/auth_service/modules/version/api/VersionControllerTest.java

@@ -0,0 +1,24 @@
+package auth_service.modules.version.api;
+
+import auth_service.modules.version.api.dto.VersionDto;
+import auth_service.shared.test.AbstractUnitTest;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class VersionControllerTest extends AbstractUnitTest {
+
+    @Test
+    void answersTheBuildOfTheImage() {
+        VersionDto version = new VersionController("4ec47f1aa0b1", "2026-09-27T08:05:00Z").getVersion().getBody();
+
+        assertEquals(new VersionDto("4ec47f1aa0b1", "2026-09-27T08:05:00Z"), version);
+    }
+
+    @Test
+    void emptyBuildArgsCountAsLocalBuild() {
+        VersionDto version = new VersionController("", "").getVersion().getBody();
+
+        assertEquals(new VersionDto("dev", null), version);
+    }
+}