add action changes for email sync

lib/membership/member.ex

@@ -48,6 +48,9 @@ defmodule Mv.Membership.Member do
                # If no user provided, that's fine (optional relationship)
                on_missing: :ignore
              )
+
+      # Override member email with user email when linking
+      change Mv.Membership.Member.Changes.OverrideEmailFromUserOnLink
     end
 
     update :update_member do
@@ -89,6 +92,11 @@ defmodule Mv.Membership.Member do
                # If no user provided, remove existing relationship (allows user removal)
                on_missing: :unrelate
              )
+
+      # Override member email with user email when linking
+      change Mv.Membership.Member.Changes.OverrideEmailFromUserOnLink
+      # Sync email changes to linked user
+      change Mv.Membership.Member.Changes.SyncEmailToUser
     end
   end
 
@@ -189,6 +197,14 @@ defmodule Mv.Membership.Member do
       constraints min_length: 1
     end
 
+    # IMPORTANT: Email Synchronization
+    # When member and user are linked, emails are automatically synced bidirectionally.
+    # User.email is the source of truth - when a link is established, member.email
+    # is overridden to match user.email. Subsequent changes to either email will
+    # sync to the other resource.
+    # See: Mv.Membership.Member.Changes.SyncEmailToUser
+    #      Mv.Membership.Member.Changes.OverrideEmailFromUserOnLink
+    #      Mv.Accounts.User.Changes.SyncEmailToMember
     attribute :email, :string do
       allow_nil? false
       constraints min_length: 5, max_length: 254