Reduce webhook delivery cleanup impact (#2550)

* Add index on webhook_deliveries.created_at

The stale scope (WHERE created_at < ?) and ordered scope
(ORDER BY created_at DESC) both benefit from this index.
Without it, Webhook::Delivery.cleanup does a full table scan.

* Run webhook delivery cleanup every 15 minutes

Each run now deletes ~15 minutes of newly-stale records instead
of ~4 hours worth, a 16x reduction in per-run write volume.

config/recurring.yml

@@ -20,7 +20,7 @@ production: &production
     schedule: every hour at minute 12
   cleanup_webhook_deliveries:
     command: "Webhook::Delivery.cleanup"
-    schedule: every 4 hours at minute 51
+    schedule: every 15 minutes
   cleanup_magic_links:
     command: "MagicLink.cleanup"
     schedule: every 4 hours

db/migrate/20260213170100_add_created_at_index_to_webhook_deliveries.rb

@@ -0,0 +1,5 @@
+class AddCreatedAtIndexToWebhookDeliveries < ActiveRecord::Migration[8.2]
+  def change
+    add_index :webhook_deliveries, :created_at
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.2].define(version: 2026_02_12_102026) do
+ActiveRecord::Schema[8.2].define(version: 2026_02_13_170100) do
   create_table "accesses", id: :uuid, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.datetime "accessed_at"
     t.uuid "account_id", null: false
@@ -821,6 +821,7 @@ ActiveRecord::Schema[8.2].define(version: 2026_02_12_102026) do
     t.datetime "updated_at", null: false
     t.uuid "webhook_id", null: false
     t.index ["account_id"], name: "index_webhook_deliveries_on_account_id"
+    t.index ["created_at"], name: "index_webhook_deliveries_on_created_at"
     t.index ["event_id"], name: "index_webhook_deliveries_on_event_id"
     t.index ["webhook_id"], name: "index_webhook_deliveries_on_webhook_id"
   end

db/schema_sqlite.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.2].define(version: 2026_02_12_102026) do
+ActiveRecord::Schema[8.2].define(version: 2026_02_13_170100) do
   create_table "accesses", id: :uuid, force: :cascade do |t|
     t.datetime "accessed_at"
     t.uuid "account_id", null: false
@@ -594,6 +594,7 @@ ActiveRecord::Schema[8.2].define(version: 2026_02_12_102026) do
     t.datetime "updated_at", null: false
     t.uuid "webhook_id", null: false
     t.index ["account_id"], name: "index_webhook_deliveries_on_account_id"
+    t.index ["created_at"], name: "index_webhook_deliveries_on_created_at"
     t.index ["event_id"], name: "index_webhook_deliveries_on_event_id"
     t.index ["webhook_id"], name: "index_webhook_deliveries_on_webhook_id"
   end