Add Stripe-based billing system

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Jason Zimdars <jz@37signals.com>

saas/db/migrate/20251203144630_create_account_subscriptions.rb

@@ -0,0 +1,15 @@
+class CreateAccountSubscriptions < ActiveRecord::Migration[8.2]
+  def change
+    create_table :account_subscriptions, id: :uuid do |t|
+      t.references :account, null: false, type: :uuid, index: true
+      t.string :plan_key
+      t.string :stripe_customer_id, null: false, index: { unique: true }
+      t.string :stripe_subscription_id, index: { unique: true }
+      t.string :status
+      t.datetime :current_period_end
+      t.datetime :cancel_at
+
+      t.timestamps
+    end
+  end
+end

saas/db/saas_schema.rb

@@ -10,7 +10,22 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.2].define(version: 2025_12_02_205753) do
+ActiveRecord::Schema[8.2].define(version: 2025_12_03_144630) do
+  create_table "account_subscriptions", id: :uuid, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.uuid "account_id", null: false
+    t.datetime "cancel_at"
+    t.datetime "created_at", null: false
+    t.datetime "current_period_end"
+    t.string "plan_key"
+    t.string "status"
+    t.string "stripe_customer_id", null: false
+    t.string "stripe_subscription_id"
+    t.datetime "updated_at", null: false
+    t.index ["account_id"], name: "index_account_subscriptions_on_account_id"
+    t.index ["stripe_customer_id"], name: "index_account_subscriptions_on_stripe_customer_id", unique: true
+    t.index ["stripe_subscription_id"], name: "index_account_subscriptions_on_stripe_subscription_id", unique: true
+  end
+
   create_table "audits1984_audits", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.uuid "auditor_id", null: false
     t.datetime "created_at", null: false