Phase 0 scaffold: arcadia-cloud Phoenix service

API-only Phoenix 1.8 project for cloud-ops, inventory, billing, and
provisioning sagas. Validates arcadia JWTs via shared Guardian secret
(verify-only; arcadia-app remains the issuer).

Deps beyond default Phoenix: guardian, cors_plug, oban, req.
Postgres on local port 5433 per arcadia stack convention.
Endpoint runs on :4005.

Endpoints:
- GET /api/health         — public, returns service identifier
- GET /api/v1/inventory   — auth-gated, returns empty list (phase 0 stub)

Oban configured with the queues phase 1+ will need:
provisioning / cloud_sync_fast|full|slow / cloud_billing / metering.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/arcadia_cloud_web/controllers/error_json.ex

@@ -0,0 +1,21 @@
+defmodule ArcadiaCloudWeb.ErrorJSON do
+  @moduledoc """
+  This module is invoked by your endpoint in case of errors on JSON requests.
+
+  See config/config.exs.
+  """
+
+  # If you want to customize a particular status code,
+  # you may add your own clauses, such as:
+  #
+  # def render("500.json", _assigns) do
+  #   %{errors: %{detail: "Internal Server Error"}}
+  # end
+
+  # By default, Phoenix returns the status message from
+  # the template name. For example, "404.json" becomes
+  # "Not Found".
+  def render(template, _assigns) do
+    %{errors: %{detail: Phoenix.Controller.status_message_from_template(template)}}
+  end
+end

lib/arcadia_cloud_web/controllers/health_controller.ex

@@ -0,0 +1,7 @@
+defmodule ArcadiaCloudWeb.HealthController do
+  use ArcadiaCloudWeb, :controller
+
+  def show(conn, _params) do
+    json(conn, %{status: "ok", service: "arcadia-cloud"})
+  end
+end

lib/arcadia_cloud_web/controllers/inventory_controller.ex

@@ -0,0 +1,12 @@
+defmodule ArcadiaCloudWeb.InventoryController do
+  @moduledoc """
+  Cloud resource inventory. Phase 0 stub — returns an empty list.
+  Phase 1 wires this to `cloud_resources` filtered by tenant scope.
+  """
+
+  use ArcadiaCloudWeb, :controller
+
+  def index(conn, _params) do
+    json(conn, %{resources: []})
+  end
+end