Phase 3: tenant invoice rollup

Month-end engine — turns a period of metered usage into tenant invoices
(revenue side). Distinct from cloud_invoices, which are DO's bills to
Sky AI (COGS).

tenant_invoices — one per (tenant, period). subtotal/tax/total cents,
status draft/issued/paid/void. unique (tenant_id, period_start).
tenant_invoice_lines — kind plan_base/addon/overage/tax, tagged with
deployment_id (NULL for tenant-level lines like GST) + resource_kind,
so the cost-vs-revenue dashboard can group by deployment and by kind.

ArcadiaCloud.Invoicing.roll_up_period/3:
- groups active subscriptions by tenant
- one tenant_invoice per tenant; per subscription, runs the quote engine
  with the deployment's ACTUAL metered usage (Metering.usage_for_period)
  and persists the recurring + overage lines tagged with the deployment
- appends a tenant-level GST line (AU 10%, per project_skyai_australia)
- idempotent on (tenant_id, period_start); re-run skips unless force:true

Because the same quote engine serves provisioning-time projection and
month-end invoicing, a tenant's quoted price and invoiced price are
computed identically.

InvoiceRollupWorker — Oban cron, 1st of month 03:00 UTC, invoices the
month just ended.

API (platform_admin sees all; tenants scoped to own):
- GET /api/v1/invoices       — tenant invoice list
- GET /api/v1/invoices/:id   — invoice with lines

Also: SubscriptionAddon now preloads its :addon so quote/invoice lines
read "Addon: storage_50gb" rather than the addon UUID.

Smoke verified: pilot deployment on Studio + storage_50gb, 3 droplets
metered across all 30 days of April (2160 droplet_hours vs 1488
included) — rollup produced an invoice with plan_base $50 + addon $7.50
+ droplet_hours overage $6.72 (672h x 1c) = $64.22 subtotal, GST $6.42,
total $70.64. Re-run without force correctly skipped.

NOT in this chunk: pushing tenant invoices to skyai-finance as AR —
that needs an income-side endpoint on skyai-finance (the phase-1 push
endpoint creates vendor expense invoices, wrong direction). Deferred to
its own chunk.

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

lib/arcadia_cloud_web/controllers/invoice_controller.ex

@@ -0,0 +1,70 @@
+defmodule ArcadiaCloudWeb.InvoiceController do
+  @moduledoc """
+  Tenant invoices (revenue side). platform_admin sees all tenants;
+  others are scoped to their own tenant_id.
+  """
+
+  use ArcadiaCloudWeb, :controller
+
+  alias ArcadiaCloud.Invoicing
+
+  def index(conn, params) do
+    identity = conn.assigns.current_identity
+
+    opts =
+      if platform_admin?(identity),
+        do: [tenant_id: params["tenant_id"], status: params["status"]],
+        else: [tenant_id: identity.tenant_id, status: params["status"]]
+
+    invoices = Invoicing.list_invoices(opts) |> Enum.map(&shape/1)
+    json(conn, %{invoices: invoices, count: length(invoices)})
+  end
+
+  def show(conn, %{"id" => id}) do
+    identity = conn.assigns.current_identity
+
+    case Invoicing.get_invoice(id) do
+      nil ->
+        conn |> put_status(:not_found) |> json(%{error: "not_found"})
+
+      invoice ->
+        if platform_admin?(identity) or invoice.tenant_id == identity.tenant_id do
+          json(conn, %{invoice: shape(invoice), lines: Enum.map(invoice.lines, &shape_line/1)})
+        else
+          conn |> put_status(:forbidden) |> json(%{error: "forbidden"})
+        end
+    end
+  end
+
+  defp platform_admin?(%{roles: roles}) when is_list(roles), do: "platform_admin" in roles
+  defp platform_admin?(_), do: false
+
+  defp shape(i) do
+    %{
+      id: i.id,
+      tenant_id: i.tenant_id,
+      period_start: i.period_start,
+      period_end: i.period_end,
+      currency: i.currency,
+      subtotal_cents: i.subtotal_cents,
+      tax_cents: i.tax_cents,
+      total_cents: i.total_cents,
+      status: i.status,
+      issued_at: i.issued_at,
+      pushed_to_finance_at: i.pushed_to_finance_at
+    }
+  end
+
+  defp shape_line(l) do
+    %{
+      kind: l.kind,
+      deployment_id: l.deployment_id,
+      resource_kind: l.resource_kind,
+      description: l.description,
+      qty: l.qty,
+      unit: l.unit,
+      unit_price_cents: l.unit_price_cents,
+      amount_cents: l.amount_cents
+    }
+  end
+end