feat: improve email copy UX with colored alerts and mailto button

- Green success alert for copied confirmation
- Blue info alert with BCC privacy tip
- Mailto button opens email program with BCC recipients
- Alerts stack vertically instead of overlapping

lib/mv_web/components/layouts.ex

@@ -65,7 +65,9 @@ defmodule MvWeb.Layouts do
 
   def flash_group(assigns) do
     ~H"""
-    <div id={@id} aria-live="polite">
+    <div id={@id} aria-live="polite" class="toast toast-top toast-end z-50 flex flex-col gap-2">
+      <.flash kind={:success} flash={@flash} />
+      <.flash kind={:warning} flash={@flash} />
       <.flash kind={:info} flash={@flash} />
       <.flash kind={:error} flash={@flash} />