Fix mobile API organizations endpoint

Fixed bug where list_user_organizations was being called with user struct
instead of user_id, causing 400 Bad Request errors.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

lib/towerops_web/controllers/api/mobile_controller.ex

@@ -33,7 +33,7 @@ defmodule ToweropsWeb.Api.MobileController do
     user = conn.assigns.current_user
 
     organizations =
-      user
+      user.id
       |> Organizations.list_user_organizations()
       |> Enum.map(fn org ->
         %{