Merge feature/quantity-default-unit-and-taken-at (add taken_at index)

db/migrate/20260402000000_add_taken_at_to_readouts.rb

@@ -1,5 +1,6 @@
 class AddTakenAtToReadouts < ActiveRecord::Migration[7.2]
   def change
     add_column :readouts, :taken_at, :datetime
+    add_index :readouts, [:user_id, :taken_at]
   end
 end

db/schema.rb

@@ -39,6 +39,7 @@ ActiveRecord::Schema[7.2].define(version: 2026_04_03_000000) do
     t.index ["quantity_id"], name: "index_readouts_on_quantity_id"
     t.index ["unit_id"], name: "index_readouts_on_unit_id"
     t.index ["user_id"], name: "index_readouts_on_user_id"
+    t.index ["user_id", "taken_at"], name: "index_readouts_on_user_id_and_taken_at"
   end
 
   create_table "units", charset: "utf8mb4", collation: "utf8mb4_0900_as_ci", force: :cascade do |t|