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.ex

@@ -0,0 +1,65 @@
+defmodule ArcadiaCloudWeb do
+  @moduledoc """
+  The entrypoint for defining your web interface, such
+  as controllers, components, channels, and so on.
+
+  This can be used in your application as:
+
+      use ArcadiaCloudWeb, :controller
+      use ArcadiaCloudWeb, :html
+
+  The definitions below will be executed for every controller,
+  component, etc, so keep them short and clean, focused
+  on imports, uses and aliases.
+
+  Do NOT define functions inside the quoted expressions
+  below. Instead, define additional modules and import
+  those modules here.
+  """
+
+  def static_paths, do: ~w(assets fonts images favicon.ico robots.txt)
+
+  def router do
+    quote do
+      use Phoenix.Router, helpers: false
+
+      # Import common connection and controller functions to use in pipelines
+      import Plug.Conn
+      import Phoenix.Controller
+    end
+  end
+
+  def channel do
+    quote do
+      use Phoenix.Channel
+    end
+  end
+
+  def controller do
+    quote do
+      use Phoenix.Controller, formats: [:html, :json]
+
+      use Gettext, backend: ArcadiaCloudWeb.Gettext
+
+      import Plug.Conn
+
+      unquote(verified_routes())
+    end
+  end
+
+  def verified_routes do
+    quote do
+      use Phoenix.VerifiedRoutes,
+        endpoint: ArcadiaCloudWeb.Endpoint,
+        router: ArcadiaCloudWeb.Router,
+        statics: ArcadiaCloudWeb.static_paths()
+    end
+  end
+
+  @doc """
+  When used, dispatch to the appropriate controller/live_view/etc.
+  """
+  defmacro __using__(which) when is_atom(which) do
+    apply(__MODULE__, which, [])
+  end
+end