docs: add @moduledoc to core membership resources

Add comprehensive module documentation to Member, Property, PropertyType, and Email.
Improves code discoverability and enables ExDoc generation.

lib/membership/member.ex

@@ -1,4 +1,36 @@
 defmodule Mv.Membership.Member do
+  @moduledoc """
+  Ash resource representing a club member.
+
+  ## Overview
+  Members are the core entity in the membership management system. Each member
+  can have:
+  - Personal information (name, email, phone, address)
+  - Optional link to a User account (1:1 relationship)
+  - Dynamic custom properties via PropertyType system
+  - Full-text searchable profile
+
+  ## Email Synchronization
+  When a member is linked to a user account, emails are automatically synchronized
+  bidirectionally. User.email is the source of truth on initial link.
+  See `Mv.EmailSync` for details.
+
+  ## Relationships
+  - `has_many :properties` - Dynamic custom fields
+  - `has_one :user` - Optional authentication account link
+
+  ## Validations
+  - Required: first_name, last_name, email
+  - 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
+  - Email uniqueness: prevents conflicts with unlinked users
+
+  ## Full-Text Search
+  Members have a `search_vector` attribute (tsvector) that is automatically
+  updated via database trigger. Search includes name, email, notes, and contact fields.
+  """
   use Ash.Resource,
     domain: Mv.Membership,
     data_layer: AshPostgres.DataLayer