Add index to leaderboards where not deleted

Based on a suggestion from pg_analyze

db/migrate/20250609143856_add_index_to_leaderboards_start_date.rb

@@ -0,0 +1,9 @@
+class AddIndexToLeaderboardsStartDate < ActiveRecord::Migration[8.0]
+  disable_ddl_transaction!
+
+  def change
+    add_index :leaderboards, :start_date,
+              where: "deleted_at IS NULL",
+              algorithm: :concurrently
+  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[8.0].define(version: 2025_06_08_205244) do
+ActiveRecord::Schema[8.0].define(version: 2025_06_09_143856) do
   create_schema "pganalyze"
 
   # These are extensions that must be enabled in order to support this database
@@ -250,6 +250,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_06_08_205244) do
     t.datetime "finished_generating_at"
     t.datetime "deleted_at"
     t.integer "period_type", default: 0, null: false
+    t.index ["start_date"], name: "index_leaderboards_on_start_date", where: "(deleted_at IS NULL)"
   end
 
   create_table "mailing_addresses", force: :cascade do |t|