feat(membership-fees): denormalize cycle_end so fee status filters run in the database

Store the cycle's end date alongside its start so the payment-status
filter can be a plain date comparison in SQL instead of loading every
cycle and classifying it in memory. The value is fixed when the cycle
is created (the fee type's interval is immutable and the update action
never changes the start date), so the denormalized column can never
drift from the computed end and needs no write-time reconciliation.

lib/membership_fees/membership_fee_cycle.ex

@@ -13,7 +13,9 @@ defmodule Mv.MembershipFees.MembershipFeeCycle do
   - `notes` - Optional notes for this cycle
 
   ## Design Decisions
-  - **No cycle_end field**: Calculated from cycle_start + interval (from fee type)
+  - **Denormalized cycle_end**: Set at create from cycle_start + interval (fee type).
+    Because the fee type interval and the cycle_start are immutable after create,
+    cycle_end never drifts, so it can be filtered/sorted in SQL.
   - **Amount stored per cycle**: Preserves historical amounts when fee type changes
   - **Calendar-aligned cycles**: All cycles start on calendar boundaries
 
@@ -46,6 +48,14 @@ defmodule Mv.MembershipFees.MembershipFeeCycle do
     create :create do
       primary? true
       accept [:cycle_start, :amount, :status, :notes, :member_id, :membership_fee_type_id]
+
+      argument :interval, :atom do
+        allow_nil? true
+
+        description "Optional pre-resolved fee-type interval; when given, SetCycleEnd skips the fee-type lookup"
+      end
+
+      change Mv.MembershipFees.MembershipFeeCycle.Changes.SetCycleEnd
     end
 
     update :update do
@@ -106,6 +116,13 @@ defmodule Mv.MembershipFees.MembershipFeeCycle do
       description "Start date of the billing cycle"
     end
 
+    attribute :cycle_end, :date do
+      allow_nil? false
+      public? true
+
+      description "Denormalized end date of the cycle (cycle_start + interval), set at create"
+    end
+
     attribute :amount, :decimal do
       allow_nil? false
       public? true