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/application.ex

@@ -0,0 +1,32 @@
+defmodule ArcadiaCloud.Application do
+  # See https://hexdocs.pm/elixir/Application.html
+  # for more information on OTP Applications
+  @moduledoc false
+
+  use Application
+
+  @impl true
+  def start(_type, _args) do
+    children = [
+      ArcadiaCloudWeb.Telemetry,
+      ArcadiaCloud.Repo,
+      {DNSCluster, query: Application.get_env(:arcadia_cloud, :dns_cluster_query) || :ignore},
+      {Phoenix.PubSub, name: ArcadiaCloud.PubSub},
+      {Oban, Application.fetch_env!(:arcadia_cloud, Oban)},
+      ArcadiaCloudWeb.Endpoint
+    ]
+
+    # See https://hexdocs.pm/elixir/Supervisor.html
+    # for other strategies and supported options
+    opts = [strategy: :one_for_one, name: ArcadiaCloud.Supervisor]
+    Supervisor.start_link(children, opts)
+  end
+
+  # Tell Phoenix to update the endpoint configuration
+  # whenever the application is updated.
+  @impl true
+  def config_change(changed, _new, removed) do
+    ArcadiaCloudWeb.Endpoint.config_change(changed, removed)
+    :ok
+  end
+end