feat: Add shared helper functions for actor handling

- Add Mv.Helpers module with ash_actor_opts/1 helper
- Add current_actor/1 with @spec to LiveHelpers
- Add ash_actor_opts/1 delegate and submit_form/3 wrapper to LiveHelpers
- Standardize actor access pattern across LiveViews

lib/mv/helpers.ex

@@ -0,0 +1,27 @@
+defmodule Mv.Helpers do
+  @moduledoc """
+  Shared helper functions used across the Mv application.
+
+  Provides utilities that are not specific to a single domain or layer.
+  """
+
+  @doc """
+  Converts an actor to Ash options list for authorization.
+  Returns empty list if actor is nil.
+
+  This helper ensures consistent actor handling across all Ash operations
+  in the application, whether called from LiveViews, changes, validations,
+  or other contexts.
+
+  ## Examples
+
+      opts = ash_actor_opts(actor)
+      Ash.read(query, opts)
+
+      opts = ash_actor_opts(nil)
+      # => []
+  """
+  @spec ash_actor_opts(Mv.Accounts.User.t() | nil) :: keyword()
+  def ash_actor_opts(nil), do: []
+  def ash_actor_opts(actor) when not is_nil(actor), do: [actor: actor]
+end