Phase 3: pricing catalog

Five catalog tables:
- plans            — plan identity (code, name); the stable thing.
- plan_versions    — versioned pricing (base_price_cents, currency,
                     status draft/active/retired). A subscription binds
                     to a version; raising prices = publish a new
                     version, existing subs unaffected until migrated.
- plan_items       — what a version includes per resource_kind, plus
                     overage terms (overage_unit, overage_price_cents,
                     hard_cap_qty).
- addons           — a la carte upgrades (code, resource_kind, qty,
                     price_cents).
- resource_prices  — effective-dated fallback per-unit pricing for
                     ad-hoc items not covered by a plan.

ArcadiaCloud.Catalog context: plan + version CRUD, active_version/1
(what a new signup gets), publish_version/1 (retires the prior active
version transactionally then activates the new one),
current_resource_price/2 (effective-dated lookup).

Seed (priv/repo/seeds/catalog_seed.exs, idempotent) creates three AUD
plans — Starter $20, Studio $50, Pro $120/mo — with included
droplet_hours / spaces_gb_month / snapshot_gb_month / bandwidth_gb /
dns_zones (and LLM token allowances on Studio + Pro), plus three storage
/ LLM addons. Prices are placeholders to tune against real DO COGS once
the cost-vs-revenue dashboard lands.

API (authenticated tenants — the catalog is what they pick from):
- GET /api/v1/catalog/plans   — plans with active version + items
- GET /api/v1/catalog/addons

Smoke verified: seed creates 3 plans + 3 addons; endpoints return the
shaped catalog.

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

lib/arcadia_cloud_web/controllers/catalog_controller.ex

@@ -0,0 +1,67 @@
+defmodule ArcadiaCloudWeb.CatalogController do
+  @moduledoc """
+  Read-only pricing catalog. Available to any authenticated tenant — the
+  catalog is what they pick a plan from. Pricing changes are operator
+  actions; no write endpoints here for MVP (seed/CLI only).
+  """
+
+  use ArcadiaCloudWeb, :controller
+
+  alias ArcadiaCloud.Catalog
+
+  def plans(conn, _params) do
+    plans =
+      Catalog.list_plans()
+      |> Enum.map(fn plan ->
+        version = Catalog.active_version(plan)
+        shape_plan(plan, version)
+      end)
+
+    json(conn, %{plans: plans})
+  end
+
+  def addons(conn, _params) do
+    addons =
+      Catalog.list_addons()
+      |> Enum.map(fn a ->
+        %{
+          code: a.code,
+          name: a.name,
+          resource_kind: a.resource_kind,
+          qty: a.qty,
+          price_cents: a.price_cents,
+          currency: a.currency
+        }
+      end)
+
+    json(conn, %{addons: addons})
+  end
+
+  defp shape_plan(plan, nil) do
+    %{code: plan.code, name: plan.name, description: plan.description, active_version: nil}
+  end
+
+  defp shape_plan(plan, version) do
+    %{
+      code: plan.code,
+      name: plan.name,
+      description: plan.description,
+      active_version: %{
+        id: version.id,
+        version: version.version,
+        base_price_cents: version.base_price_cents,
+        currency: version.currency,
+        items:
+          Enum.map(version.items, fn i ->
+            %{
+              resource_kind: i.resource_kind,
+              included_qty: i.included_qty,
+              overage_unit: i.overage_unit,
+              overage_price_cents: i.overage_price_cents,
+              hard_cap_qty: i.hard_cap_qty
+            }
+          end)
+      }
+    }
+  end
+end