fix: add missing validate_amount_format function

- Function was referenced but not defined
- Cleans invalid characters from amount input
- Provides better UX by sanitizing input

lib/mv_web/live/membership_fee_type_live/form.ex

@@ -328,6 +328,34 @@ defmodule MvWeb.MembershipFeeTypeLive.Form do
     assign(socket, form: to_form(form))
   end
 
+  # Validates amount format and cleans invalid characters
+  defp validate_amount_format(params) do
+    case Map.get(params, "amount") do
+      nil -> params
+      "" -> params
+      amount_str when is_binary(amount_str) ->
+        # Check if it's a valid number format
+        case Decimal.parse(amount_str) do
+          {_decimal, ""} ->
+            # Valid decimal
+            params
+
+          {_decimal, _rest} ->
+            # Has trailing characters - invalid, but let Ash handle validation
+            params
+
+          :error ->
+            # Not a valid number - try to clean it up
+            # Remove non-numeric characters except decimal point
+            cleaned = String.replace(amount_str, ~r/[^\d.]/, "")
+            Map.put(params, "amount", cleaned)
+        end
+
+      _ ->
+        params
+    end
+  end
+
   # Helper to extract existing form values to preserve them when only one field changes
   defp get_existing_form_values(form) do
     # Extract values directly from form fields to get current state