add analytics CSV export

Downloads a ZIP with one CSV per report (overview, trend, pages, entry/exit
pages, sources, referrers, countries, devices, funnel). Export button lives
next to the period selector and picks up the current period and any active
filters using a JS hook + JS.set_attribute, so the downloaded data always
matches what's on screen.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/js/app.js

@@ -509,6 +509,31 @@ const CardRadioScroll = {
   }
 }
 
+// Analytics export: reads the current period and filters from the DOM at click time
+// so the download URL is always correct, even if clicked before the LiveView re-render.
+const AnalyticsExport = {
+  mounted() {
+    this.el.addEventListener("click", (e) => {
+      e.preventDefault()
+      const params = new URLSearchParams()
+      params.set("period", this.el.getAttribute("data-period") || "30d")
+      document.querySelectorAll("[data-filter-dimension]").forEach((span) => {
+        const dim = span.getAttribute("data-filter-dimension")
+        const val = span.getAttribute("data-filter-value")
+        if (dim && val) params.set(`filter[${dim}]`, val)
+      })
+      // Use a temporary anchor click so the download doesn't navigate away and
+      // kill the LiveView WebSocket.
+      const a = document.createElement("a")
+      a.href = `/admin/analytics/export?${params}`
+      a.download = ""
+      document.body.appendChild(a)
+      a.click()
+      document.body.removeChild(a)
+    })
+  }
+}
+
 // Analytics: send screen width for device classification (Layer 3)
 const AnalyticsInit = {
   mounted() {
@@ -592,7 +617,7 @@ const ChartTooltip = {
 const csrfToken = document.querySelector("meta[name='csrf-token']").getAttribute("content")
 const liveSocket = new LiveSocket("/live", Socket, {
   params: {_csrf_token: csrfToken, screen_width: window.innerWidth},
-  hooks: {...colocatedHooks, ColorSync, Lightbox, CartPersist, CartDrawer, ProductImageScroll, SearchModal, CollectionFilters, CardRadioScroll, AnalyticsInit, ChartTooltip},
+  hooks: {...colocatedHooks, ColorSync, Lightbox, CartPersist, CartDrawer, ProductImageScroll, SearchModal, CollectionFilters, CardRadioScroll, AnalyticsInit, AnalyticsExport, ChartTooltip},
 })
 
 // Show progress bar on live navigation and form submits