refactor(member-live): modularize the overview and drop the superseded in-memory paths

Extract the cookie parser, export-payload builder and fee-status helper
into their own modules and remove the filter/sort/load helpers the
database pushdown made dead, so the overview LiveView stays a thin
coordinator over focused units.

lib/mv_web/live/member_live/index/field_selection.ex

@@ -29,6 +29,8 @@ defmodule MvWeb.MemberLive.Index.FieldSelection do
   Comma-separated list: `?fields=first_name,email,custom_field_abc-123`
   """
 
+  alias MvWeb.MemberLive.Index.Cookie
+
   @cookie_name "member_field_selection"
   @cookie_max_age 365 * 24 * 60 * 60
   @session_key "member_field_selection"
@@ -80,7 +82,7 @@ defmodule MvWeb.MemberLive.Index.FieldSelection do
         %{}
 
       [cookie_header | _rest] ->
-        cookies = parse_cookie_header(cookie_header)
+        cookies = Cookie.parse_header(cookie_header)
 
         case Map.get(cookies, @cookie_name) do
           nil -> %{}
@@ -90,19 +92,6 @@ defmodule MvWeb.MemberLive.Index.FieldSelection do
     end
   end
 
-  # Parses cookie header string into a map
-  defp parse_cookie_header(cookie_header) when is_binary(cookie_header) do
-    cookie_header
-    |> String.split(";")
-    |> Enum.map(&String.trim/1)
-    |> Enum.map(&String.split(&1, "=", parts: 2))
-    |> Enum.reduce(%{}, fn
-      [key, value], acc -> Map.put(acc, key, URI.decode(value))
-      [key], acc -> Map.put(acc, key, "")
-      _, acc -> acc
-    end)
-  end
-
   @doc """
   Saves field selection to cookie.