Phase 3: deployment model + subscriptions

cloud_deployments — the billable unit (one app instance). A tenant has
1..N deployments; cloud_resources.deployment_id ties resources to one.
Fields: tenant_id, slug (unique per tenant), display_name, region,
state, llm_mode, billing_action_suspended (operator override),
template_code/version (nullable — formal templates land in phase 4).

Lifecycle state machine in ArcadiaCloud.Deployments — states trial /
active / past_due / paused / suspended / cancelled / archived. Every
transition is validated against an explicit @transitions map and
recorded in cloud_deployment_events. create_deployment defaults to
`active` (trial is wired but no flow enters it yet).

subscriptions — one per deployment, binds it to a plan_version. status
active/paused/cancelled, current period dates, trial_ends_at.

subscription_addons — addons attached to a subscription with price + qty
SNAPSHOTTED at attach time, so a later catalog price change can't
retroactively reprice an existing subscriber.

ArcadiaCloud.Subscriptions context: create_subscription (period defaults
to current calendar month), attach_addon (snapshots from the live Addon),
change_plan_version (migrate to a new version — price changes / up-down
grades), get_subscription_for_deployment.

API (platform_admin sees all tenants; others scoped to own tenant_id):
- GET/POST /api/v1/deployments
- GET      /api/v1/deployments/:id            (with subscription + events)
- POST     /api/v1/deployments/:id/transition
- POST     /api/v1/deployments/:id/subscribe  (plan_code + optional addons)

Smoke verified: created a deployment, transitioned active->paused
(events logged with actor), rejected an invalid paused->archived
transition (422), subscribed to Studio with the storage_50gb addon —
addon price snapshotted at 750c/qty 50; show returns deployment +
subscription + event history.

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

lib/arcadia_cloud_web/router.ex

@@ -28,5 +28,11 @@ defmodule ArcadiaCloudWeb.Router do
 
     get "/catalog/plans", CatalogController, :plans
     get "/catalog/addons", CatalogController, :addons
+
+    get "/deployments", DeploymentController, :index
+    post "/deployments", DeploymentController, :create
+    get "/deployments/:id", DeploymentController, :show
+    post "/deployments/:id/transition", DeploymentController, :transition
+    post "/deployments/:id/subscribe", DeploymentController, :subscribe
   end
 end