feat: Add Dependency record for health responses

Author: thced

src/main/java/com/retailsvc/http/Dependency.java

@@ -0,0 +1,17 @@
+package com.retailsvc.http;
+
+import java.util.Objects;
+
+/**
+ * A single dependency entry within a {@link HealthOutcome}.
+ *
+ * @param id stable identifier of the dependency (e.g. {@code "jdbc"})
+ * @param status free-form status; {@code "Up"} (case-insensitive) is treated as healthy by {@link
+ *     HealthOutcome#isUp()}; any other value is treated as unhealthy
+ */
+public record Dependency(String id, String status) {
+  public Dependency {
+    Objects.requireNonNull(id, "id");
+    Objects.requireNonNull(status, "status");
+  }
+}

src/test/java/com/retailsvc/http/DependencyTest.java

@@ -0,0 +1,30 @@
+package com.retailsvc.http;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNullPointerException;
+
+import org.junit.jupiter.api.Test;
+
+class DependencyTest {
+
+  @Test
+  void holdsIdAndStatus() {
+    Dependency d = new Dependency("jdbc", "Up");
+    assertThat(d.id()).isEqualTo("jdbc");
+    assertThat(d.status()).isEqualTo("Up");
+  }
+
+  @Test
+  void rejectsNullId() {
+    assertThatNullPointerException()
+        .isThrownBy(() -> new Dependency(null, "Up"))
+        .withMessageContaining("id");
+  }
+
+  @Test
+  void rejectsNullStatus() {
+    assertThatNullPointerException()
+        .isThrownBy(() -> new Dependency("jdbc", null))
+        .withMessageContaining("status");
+  }
+}