feat: add Umami analytics helper and window type declaration

lib/analytics.ts

@@ -0,0 +1,21 @@
+import type { BuilderSlotKey } from "@/types/builderSlots";
+
+export function trackBuildStarted() {
+  window.umami?.track("build_started");
+}
+
+export function trackPartSelected(slot: BuilderSlotKey, partName: string, partId: string) {
+  window.umami?.track("part_selected", { slot, part_name: partName, part_id: partId });
+}
+
+export function trackAffiliateLinkClicked(partName: string, retailer: string) {
+  window.umami?.track("affiliate_link_clicked", { part_name: partName, retailer });
+}
+
+export function trackBuildShared() {
+  window.umami?.track("build_shared");
+}
+
+export function trackBuildSaved() {
+  window.umami?.track("build_saved");
+}

types/umami.d.ts

@@ -0,0 +1,5 @@
+interface Window {
+  umami?: {
+    track: (eventName: string, properties?: Record<string, string | number | boolean>) => void;
+  };
+}