Phase 1 cost ingestion: balance + invoices + CSV parse + resource match

Three new schemas:
- cloud_balance_snapshots — hourly MTD balance/usage poll for live-accrual.
- cloud_invoices — header per provider invoice, with ingest status flags.
- cloud_cost_lines — per-line-item COGS, FK to cloud_resources where matched.

Three new Oban workers (queue: cloud_billing):
- BalanceWorker (hourly) records a snapshot.
- BillingHistoryWorker (daily) discovers invoices via /v2/customers/my/
  billing_history, upserts headers, enqueues an InvoiceIngestWorker for
  each not-yet-ingested invoice.
- InvoiceIngestWorker (per-invoice) fetches /invoices/:uuid/csv, parses
  with NimbleCSV (header-keyed so column order shifts don't break us),
  replaces the invoice's line set, then matches lines to cloud_resources
  by (kind, name) — case-insensitive, name extracted from "name (size)"
  description format.

DigitalOcean.Client gains get_balance / list_billing_history /
get_invoice_summary / fetch_invoice_csv. The CSV endpoint returns text/csv
so we bypass Req's body decoder.

Cron additions: BalanceWorker hourly at :07, BillingHistoryWorker daily
at 02:23.

API:
- GET /api/v1/billing/balance — latest snapshot, platform_admin only.
- GET /api/v1/billing/cost-lines?period=YYYY-MM-DD&kind&limit — per-line
  COGS, platform_admin only.

Live smoke against real DO billing API surfaced and fixed three CSV-format
gotchas: column headers use underscores not spaces (group_description,
project_name), USD column has $ prefix, dates use "YYYY-MM-DD HH:MM:SS
+0000" format (space separator + RFC822 offset).

Verified: 137 historical invoices discovered going back to 2014;
April 2026 invoice (33 lines, $86.92 total) ingested with 6/33 lines
matched to current cloud_resources. Unmatched lines are correctly
historic droplets, Spaces buckets (not yet synced), and GST.

NimbleCSV ~> 1.2 added as a dep.

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

lib/arcadia_cloud/sync/billing_history_worker.ex

@@ -0,0 +1,97 @@
+defmodule ArcadiaCloud.Sync.BillingHistoryWorker do
+  @moduledoc """
+  Daily discovery of new invoices via `/v2/customers/my/billing_history`.
+
+  Upserts an invoice header per row and enqueues an InvoiceIngestWorker
+  job for any invoice not yet ingested (CSV parse + line-item write +
+  resource match). Idempotent — re-running re-enqueues nothing new.
+  """
+
+  use Oban.Worker, queue: :cloud_billing, max_attempts: 3
+
+  alias ArcadiaCloud.Billing
+  alias ArcadiaCloud.DigitalOcean.Client
+  alias ArcadiaCloud.Sync.InvoiceIngestWorker
+
+  @impl Oban.Worker
+  def perform(_job) do
+    with {:ok, history} <- Client.list_billing_history() do
+      Enum.each(history, fn item ->
+        case extract_invoice_attrs(item) do
+          {:ok, attrs} ->
+            {:ok, invoice} = Billing.upsert_invoice(attrs)
+
+            if is_nil(invoice.lines_ingested_at) do
+              %{invoice_id: invoice.id}
+              |> InvoiceIngestWorker.new()
+              |> Oban.insert!()
+            end
+
+          :skip ->
+            :ok
+        end
+      end)
+
+      :ok
+    end
+  end
+
+  # DO billing_history items have shape:
+  #   {"type" => "Invoice", "description" => "Invoice for September 2024",
+  #    "amount" => "-100.00", "date" => "2024-10-01T00:00:00Z",
+  #    "invoice_id" => "uuid-here", "invoice_uuid" => "uuid-here"}
+  # We only care about Invoice rows (skip Payment, Credit, etc).
+  defp extract_invoice_attrs(%{"type" => "Invoice"} = item) do
+    case item["invoice_uuid"] || item["invoice_id"] do
+      nil ->
+        :skip
+
+      uuid ->
+        {:ok,
+         %{
+           provider: "digitalocean",
+           provider_invoice_id: uuid,
+           invoice_period: derive_period(item["date"]),
+           amount_cents: dollars_to_cents_abs(item["amount"]),
+           status: "issued",
+           issued_at: parse_iso(item["date"]),
+           raw: item
+         }}
+    end
+  end
+
+  defp extract_invoice_attrs(_), do: :skip
+
+  # Invoice dated YYYY-MM-01 covers the previous month. Derive period as
+  # first-of-the-previous-month.
+  defp derive_period(nil), do: Date.utc_today() |> Date.add(-30) |> first_of_month()
+
+  defp derive_period(iso) do
+    case DateTime.from_iso8601(iso) do
+      {:ok, dt, _} -> dt |> DateTime.to_date() |> Date.add(-1) |> first_of_month()
+      _ -> Date.utc_today() |> first_of_month()
+    end
+  end
+
+  defp first_of_month(%Date{year: y, month: m}), do: Date.new!(y, m, 1)
+
+  defp dollars_to_cents_abs(nil), do: nil
+
+  defp dollars_to_cents_abs(value) when is_binary(value) do
+    case Float.parse(value) do
+      {float, _} -> abs(round(float * 100))
+      :error -> nil
+    end
+  end
+
+  defp dollars_to_cents_abs(value) when is_number(value), do: abs(round(value * 100))
+
+  defp parse_iso(nil), do: nil
+
+  defp parse_iso(str) when is_binary(str) do
+    case DateTime.from_iso8601(str) do
+      {:ok, dt, _} -> DateTime.truncate(dt, :second)
+      _ -> nil
+    end
+  end
+end