Add DNS lookup tool and tests

public/styles.css

@@ -233,4 +233,112 @@ button:disabled {
   button {
     width: 100%;
   }
-}
+}
+.site-header {
+  width: min(760px, 100%);
+  margin-bottom: 18px;
+}
+
+.site-header h1 {
+  margin-bottom: 10px;
+}
+
+.tool-tabs {
+  display: flex;
+  width: min(760px, 100%);
+  gap: 8px;
+  margin-bottom: 14px;
+}
+
+.tool-tab {
+  padding: 10px 14px;
+  border: 1px solid var(--border);
+  background: #0d1523;
+  color: var(--muted);
+}
+
+.tool-tab:hover {
+  background: var(--surface-light);
+  color: var(--text);
+}
+
+.tool-tab.active {
+  border-color: var(--accent);
+  background: rgba(76, 166, 255, 0.12);
+  color: var(--accent);
+}
+
+.tool-header h2 {
+  margin-bottom: 8px;
+  font-size: 1.6rem;
+}
+
+.tool-description {
+  margin-bottom: 24px;
+  color: var(--muted);
+  line-height: 1.6;
+}
+
+.hostname-badge {
+  padding: 5px 10px;
+  border-radius: 999px;
+  background: rgba(76, 166, 255, 0.12);
+  color: var(--accent);
+  font-size: 0.82rem;
+  font-weight: 700;
+  overflow-wrap: anywhere;
+}
+
+.dns-records {
+  display: grid;
+  gap: 12px;
+}
+
+.dns-record-group {
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  background: #0d1523;
+  overflow: hidden;
+}
+
+.dns-record-group h4 {
+  margin: 0;
+  padding: 11px 14px;
+  border-bottom: 1px solid var(--border);
+  color: var(--accent);
+  font-size: 0.9rem;
+  letter-spacing: 0.08em;
+}
+
+.dns-record-list {
+  margin: 0;
+  padding: 12px 14px 12px 34px;
+}
+
+.dns-record-list li {
+  margin: 5px 0;
+  overflow-wrap: anywhere;
+}
+
+.empty-record {
+  margin: 0;
+  padding: 12px 14px;
+  color: var(--muted);
+}
+
+.dns-checked-at {
+  margin: 14px 0 0;
+  color: var(--muted);
+  font-size: 0.84rem;
+}
+
+@media (max-width: 640px) {
+  .tool-tabs {
+    display: grid;
+    grid-template-columns: 1fr 1fr;
+  }
+
+  .tool-tab {
+    width: 100%;
+  }
+}