feat(vereinfacht): add client, sync flash and SyncContact change

- Application: create SyncFlash ETS table on start
- Vereinfacht: Client, SyncFlash, sync_member, format_error, sync_members_without_contact
- SyncContact change on Member create_member and update_member
- Member: attribute vereinfacht_contact_id, internal action set_vereinfacht_contact_id

lib/membership/member.ex

@@ -117,6 +117,9 @@ defmodule Mv.Membership.Member do
       # Requires both join_date and membership_fee_type_id to be present
       change Mv.MembershipFees.Changes.SetMembershipFeeStartDate
 
+      # Sync member to Vereinfacht as finance contact (if configured)
+      change Mv.Vereinfacht.Changes.SyncContact
+
       # Trigger cycle generation after member creation
       # Only runs if membership_fee_type_id is set
       # Note: Cycle generation runs asynchronously to not block the action,
@@ -190,6 +193,9 @@ defmodule Mv.Membership.Member do
         where [changing(:membership_fee_type_id)]
       end
 
+      # Sync member to Vereinfacht as finance contact (if configured)
+      change Mv.Vereinfacht.Changes.SyncContact
+
       # Trigger cycle regeneration when membership_fee_type_id changes
       # This deletes future unpaid cycles and regenerates them with the new type/amount
       # Note: Cycle regeneration runs synchronously in the same transaction to ensure atomicity
@@ -243,6 +249,13 @@ defmodule Mv.Membership.Member do
              end)
     end
 
+    # Internal: set vereinfacht_contact_id after syncing with Vereinfacht API.
+    # Not exposed via code interface; used only by Mv.Vereinfacht.Changes.SyncContact.
+    update :set_vereinfacht_contact_id do
+      require_atomic? false
+      accept [:vereinfacht_contact_id]
+    end
+
     # Action to handle fuzzy search on specific fields
     read :search do
       argument :query, :string, allow_nil?: true
@@ -320,6 +333,12 @@ defmodule Mv.Membership.Member do
       authorize_if Mv.Authorization.Checks.HasPermission
     end
 
+    # Internal sync action: allow setting vereinfacht_contact_id (used only by SyncContact change).
+    policy action(:set_vereinfacht_contact_id) do
+      description "Allow internal sync to set Vereinfacht contact ID"
+      authorize_if always()
+    end
+
     # CREATE/UPDATE: Forbid member–user link unless admin, then check permissions
     # ForbidMemberUserLinkUnlessAdmin: only admins may pass :user (link or unlink via nil/empty).
     # HasPermission: :own_data → update linked; :read_only → no update; :normal_user/admin → update all.
@@ -593,6 +612,14 @@ defmodule Mv.Membership.Member do
       public? true
       description "Date from which membership fees should be calculated"
     end
+
+    # Vereinfacht accounting software integration: ID of the finance contact synced via API.
+    # Set by Mv.Vereinfacht.Changes.SyncContact; not accepted in create/update actions.
+    attribute :vereinfacht_contact_id, :string do
+      allow_nil? true
+      public? true
+      description "ID of the finance contact in Vereinfacht (set by sync)"
+    end
   end
 
   relationships do
@@ -1275,7 +1302,10 @@ defmodule Mv.Membership.Member do
 
   # Extracts custom field values from existing member data (update scenario)
   defp extract_existing_values(member_data, changeset) do
-    actor = Map.get(changeset.context, :actor)
+    actor =
+      Map.get(changeset.context, :actor) ||
+        Mv.Helpers.SystemActor.get_system_actor()
+
     opts = Helpers.ash_actor_opts(actor)
 
     case Ash.load(member_data, :custom_field_values, opts) do