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/email.ex

@@ -1,4 +1,37 @@
 defmodule Mv.Membership.Email do
+  @moduledoc """
+  Custom Ash type for validated email addresses.
+
+  ## Overview
+  This type extends `:string` with email-specific validation constraints.
+  It ensures that email values stored in Property resources are valid email
+  addresses according to a standard regex pattern.
+
+  ## Validation Rules
+  - Minimum length: 5 characters
+  - Maximum length: 254 characters (RFC 5321 maximum)
+  - Pattern: Standard email format (username@domain.tld)
+  - Automatic trimming of leading/trailing whitespace
+
+  ## Usage
+  This type is used in the Property union type for properties with
+  `value_type: :email` in PropertyType definitions.
+
+  ## Example
+      # In a property type definition
+      PropertyType.create!(%{
+        name: "work_email",
+        value_type: :email
+      })
+
+      # Valid values
+      "user@example.com"
+      "first.last@company.co.uk"
+
+      # Invalid values
+      "not-an-email"      # Missing @ and domain
+      "a@b"               # Too short
+  """
   @match_pattern ~S/^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$/
   @match_regex Regex.compile!(@match_pattern)
   @min_length 5