refactor: remove manual amount validation, use Ash default validation

- Remove validate_amount_format function - Ash handles Decimal validation automatically
- Remove oninput and pattern attributes - not needed with Ash validation
- Simplify validate handler - let AshPhoenix.Form.validate do its job
- Follows Ash best practices for form validation

lib/mv_web/live/membership_fee_type_live/form.ex

@@ -46,9 +46,6 @@ defmodule MvWeb.MembershipFeeTypeLive.Form do
           label={gettext("Amount")}
           step="0.01"
           min="0"
-          pattern="[0-9]+(\.[0-9]{1,2})?"
-          phx-debounce="blur"
-          oninput="this.setCustomValidity(''); if (!this.validity.valid) { this.setCustomValidity('Please enter a valid number'); }"
           required
         />
 
@@ -210,9 +207,6 @@ defmodule MvWeb.MembershipFeeTypeLive.Form do
 
   @impl true
   def handle_event("validate", %{"membership_fee_type" => params}, socket) do
-    # Validate amount format if present
-    params = validate_amount_format(params)
-
     # Merge with existing form values to preserve unchanged fields
     # Extract values directly from form fields to get current state
     existing_values = get_existing_form_values(socket.assigns.form)
@@ -231,6 +225,7 @@ defmodule MvWeb.MembershipFeeTypeLive.Form do
         merged_params
       end
 
+    # Let Ash handle validation automatically - it will validate Decimal format
     validated_form = AshPhoenix.Form.validate(socket.assigns.form, merged_params)
 
     # Check if amount changed on edit