docs: enable Credo ModuleDoc check and fix remaining modules

Add @moduledoc to Secrets, LiveHelpers, AuthOverrides, and Membership domain.
Enable Credo.Check.Readability.ModuleDoc in .credo.exs.

lib/membership/membership.ex

@@ -1,4 +1,21 @@
 defmodule Mv.Membership do
+  @moduledoc """
+  Ash Domain for membership management.
+
+  ## Resources
+  - `Member` - Club members with personal information and custom properties
+  - `Property` - Dynamic custom field values attached to members
+  - `PropertyType` - Schema definitions for custom properties
+
+  ## Public API
+  The domain exposes these main actions:
+  - Member CRUD: `create_member/1`, `list_members/0`, `update_member/2`, `destroy_member/1`
+  - Property management: `create_property/1`, `list_property/0`, etc.
+  - PropertyType management: `create_property_type/1`, `list_property_types/0`, etc.
+
+  ## Admin Interface
+  The domain is configured with AshAdmin for management UI.
+  """
   use Ash.Domain,
     extensions: [AshAdmin.Domain, AshPhoenix]
 

lib/mv/secrets.ex

@@ -1,4 +1,23 @@
 defmodule Mv.Secrets do
+  @moduledoc """
+  Secret provider for AshAuthentication.
+
+  ## Purpose
+  Provides runtime configuration secrets for Ash Authentication strategies,
+  particularly for OIDC (Rauthy) authentication.
+
+  ## Configuration Source
+  Secrets are read from the `:rauthy` key in the application configuration,
+  which is typically set in `config/runtime.exs` from environment variables:
+  - `OIDC_CLIENT_ID`
+  - `OIDC_CLIENT_SECRET`
+  - `OIDC_BASE_URL`
+  - `OIDC_REDIRECT_URI`
+
+  ## Usage
+  This module is automatically called by AshAuthentication when resolving
+  secrets for the User resource's OIDC strategy.
+  """
   use AshAuthentication.Secret
 
   def secret_for(

lib/mv_web/auth_overrides.ex

@@ -1,4 +1,16 @@
 defmodule MvWeb.AuthOverrides do
+  @moduledoc """
+  UI customizations for AshAuthentication Phoenix components.
+
+  ## Overrides
+  - `SignIn` - Restricts form width to prevent full-width display
+  - `Banner` - Replaces default logo with "Mitgliederverwaltung" text
+  - `HorizontalRule` - Translates "or" text to German
+
+  ## Documentation
+  For complete reference on available overrides, see:
+  https://hexdocs.pm/ash_authentication_phoenix/ui-overrides.html
+  """
   use AshAuthentication.Phoenix.Overrides
   use Gettext, backend: MvWeb.Gettext
 

lib/mv_web/live_helpers.ex

@@ -1,4 +1,16 @@
 defmodule MvWeb.LiveHelpers do
+  @moduledoc """
+  Shared LiveView lifecycle hooks and helper functions.
+
+  ## on_mount Hooks
+  - `:default` - Sets the user's locale from session (defaults to "de")
+
+  ## Usage
+  Add to LiveView modules via:
+  ```elixir
+  on_mount {MvWeb.LiveHelpers, :default}
+  ```
+  """
   def on_mount(:default, _params, session, socket) do
     locale = session["locale"] || "de"
     Gettext.put_locale(locale)