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/property.ex

@@ -1,4 +1,36 @@
 defmodule Mv.Membership.Property do
+  @moduledoc """
+  Ash resource representing a custom property value for a member.
+
+  ## Overview
+  Properties implement the Entity-Attribute-Value (EAV) pattern, allowing
+  dynamic custom fields to be attached to members. Each property links a
+  member to a property type and stores the actual value.
+
+  ## Value Storage
+  Values are stored using Ash's union type with JSONB storage format:
+  ```json
+  {
+    "type": "string",
+    "value": "example"
+  }
+  ```
+
+  ## Supported Types
+  - `:string` - Text data
+  - `:integer` - Numeric data
+  - `:boolean` - True/false flags
+  - `:date` - Date values
+  - `:email` - Validated email addresses (custom type)
+
+  ## Relationships
+  - `belongs_to :member` - The member this property belongs to (CASCADE delete)
+  - `belongs_to :property_type` - The property type definition
+
+  ## Constraints
+  - Each member can have only one property per property type (unique composite index)
+  - Properties are deleted when the associated member is deleted (CASCADE)
+  """
   use Ash.Resource,
     domain: Mv.Membership,
     data_layer: AshPostgres.DataLayer