feat: implement backend API clients for multi-marketplace integration and frontend service layer

frontend/css/styles.css

@@ -162,3 +162,82 @@ label textarea {
   border-radius: var(--radius);
   box-shadow: var(--shadow);
 }
+
+.tabs-container {
+  display: flex;
+  justify-content: center;
+  gap: 1rem;
+  padding: 1rem;
+  background: var(--color-surface);
+  border-bottom: 1px solid hsla(0,0%,100%,0.1);
+}
+
+.tab-btn {
+  background: transparent;
+  color: var(--color-text);
+  border: none;
+  padding: 0.5rem 1rem;
+  font-size: 1.1rem;
+  cursor: pointer;
+  border-bottom: 2px solid transparent;
+  transition: all 0.2s;
+}
+
+.tab-btn:hover {
+  color: var(--color-primary);
+}
+
+.tab-btn.active {
+  color: var(--color-primary);
+  border-bottom: 2px solid var(--color-primary);
+}
+
+.platforms-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
+  gap: 1.5rem;
+}
+
+.platform-card {
+  background: var(--color-surface);
+  padding: 1.5rem;
+  border-radius: var(--radius);
+  border: 1px solid hsla(0,0%,100%,0.1);
+  transition: transform 0.2s;
+}
+
+.platform-card:hover {
+  transform: translateY(-2px);
+}
+
+.platform-card h3 {
+  color: var(--color-primary);
+  margin-bottom: 0.5rem;
+}
+
+.platform-card .status {
+  font-size: 0.9rem;
+  margin-bottom: 1rem;
+}
+
+.active-platform {
+  border-color: var(--color-success);
+}
+
+.active-platform h3 {
+  color: var(--color-success);
+}
+
+.platform-form {
+  display: flex;
+  flex-direction: column;
+  gap: 0.5rem;
+}
+
+.platform-form input {
+  padding: 0.5rem;
+  border: 1px solid hsla(0,0%,100%,0.1);
+  border-radius: var(--radius);
+  background: rgba(0,0,0,0.2);
+  color: #fff;
+}