feat: remove birth_date field from Member resource

Users who need birthday data can use custom fields instead.
Closes #161

lib/membership/member.ex

@@ -24,7 +24,7 @@ defmodule Mv.Membership.Member do
   - Email format validation (using EctoCommons.EmailValidator)
   - Phone number format: international format with 6-20 digits
   - Postal code format: exactly 5 digits (German format)
-  - Date validations: birth_date and join_date not in future, exit_date after join_date
+  - Date validations: join_date not in future, exit_date after join_date
   - Email uniqueness: prevents conflicts with unlinked users
 
   ## Full-Text Search
@@ -284,11 +284,6 @@ defmodule Mv.Membership.Member do
       end
     end
 
-    # Birth date not in the future
-    validate compare(:birth_date, less_than_or_equal_to: &Date.utc_today/0),
-      where: [present(:birth_date)],
-      message: "cannot be in the future"
-
     # Join date not in the future
     validate compare(:join_date, less_than_or_equal_to: &Date.utc_today/0),
       where: [present(:join_date)],
@@ -351,10 +346,6 @@ defmodule Mv.Membership.Member do
       constraints min_length: 5, max_length: 254
     end
 
-    attribute :birth_date, :date do
-      allow_nil? true
-    end
-
     attribute :paid, :boolean do
       allow_nil? true
     end