add admin email settings page with provider selection

Card radio component for picking email providers (SMTP, SendGrid, Mailjet, etc.)
with instant client-side switching via JS hook. Adapter configs are pre-rendered
and toggled without a server round-trip. Secrets are preserved when re-saving
with blank password fields. Includes from address field, test email sending,
and disconnect flow.

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

assets/js/app.js

@@ -487,10 +487,32 @@ const CollectionFilters = {
   }
 }
 
+const CardRadioScroll = {
+  mounted() {
+    this.el.addEventListener("change", (e) => {
+      if (!e.target.matches('input[type="radio"]')) return
+      const key = e.target.value
+      const form = this.el.closest("form")
+      if (!form) return
+
+      form.querySelectorAll("[data-adapter]").forEach((section) => {
+        const match = section.dataset.adapter === key
+        section.hidden = !match
+        section.querySelectorAll("input, textarea, select, button[type='submit']").forEach((input) => {
+          input.disabled = !match
+        })
+      })
+
+      const target = document.getElementById(`adapter-config-${key}`)
+      if (target) target.scrollIntoView({ behavior: "smooth", block: "nearest" })
+    })
+  }
+}
+
 const csrfToken = document.querySelector("meta[name='csrf-token']").getAttribute("content")
 const liveSocket = new LiveSocket("/live", Socket, {
   params: {_csrf_token: csrfToken},
-  hooks: {...colocatedHooks, ColorSync, Lightbox, CartPersist, CartDrawer, ProductImageScroll, SearchModal, CollectionFilters},
+  hooks: {...colocatedHooks, ColorSync, Lightbox, CartPersist, CartDrawer, ProductImageScroll, SearchModal, CollectionFilters, CardRadioScroll},
 })
 
 // Show progress bar on live navigation and form submits