Setting: remove unused actor in default_fee_type validation

- Docs: Regenerate Cycles server-side enforcement note in membership-fee-architecture.

docs/membership-fee-architecture.md

@@ -340,7 +340,7 @@ lib/
 
 - **MembershipFeeType:** All permission sets can read (:all); only admin has create/update/destroy (:all).
 - **MembershipFeeCycle:** All can read (:all); read_only has read only; normal_user and admin have read + create + update + destroy (:all).
-- **Manual "Regenerate Cycles" (UI):** The "Regenerate Cycles" button in the member detail view is shown to users who have MembershipFeeCycle create permission (normal_user and admin). Regeneration runs with system actor; UI access is gated by `can_create_cycle`.
+- **Manual "Regenerate Cycles" (UI + server):** The "Regenerate Cycles" button in the member detail view is shown to users who have MembershipFeeCycle create permission (normal_user and admin). UI access is gated by `can_create_cycle`. The LiveView handler also enforces `can?(:create, MembershipFeeCycle)` server-side before running regeneration (so e.g. a read_only user cannot trigger it via DevTools). Regeneration runs with system actor.
 
 **Resource Policies:**
 

lib/membership/setting.ex

@@ -160,14 +160,6 @@ defmodule Mv.Membership.Setting do
                  Ash.Changeset.get_attribute(changeset, :default_membership_fee_type_id)
 
                if fee_type_id do
-                 # Actor may be in changeset.context (action context) or validation context
-                 ctx = changeset.context || %{}
-
-                 actor =
-                   get_in(ctx, [:private, :actor]) ||
-                     Map.get(ctx, :actor) ||
-                     (context && Map.get(context, :actor))
-
                  # Check existence only; action is already restricted by policy (e.g. admin).
                  opts = [domain: Mv.MembershipFees, authorize?: false]