Fix Zatladder fallback and OTP drift tolerance

[Copilot]

Checklist

• Merged database migrations into 1 database migration.
• Tested database migrations from origin/staging (git checkout staging ; git pull ; bundle exec rails db:reset ; git checkout BRANCH ; bundle exec rails db:migrate).

Summary

Fixes two issues and adds a database migration to resolve schema inconsistency:

Zatladder Controller: When no Amber users exist, fallback to sofia_account users instead of crashing:

users = User.in_amber.any? ? User.in_amber : User.sofia_account
@users_spendings = users.calculate_spendings(from:, to:)

OTP Authentication: Accept 1-period drift to handle clock skew between client and server:

sofia_account.authenticate_otp(params[:verification_code], drift: 1)

Database Migration: Adds order_total column back to orders table if missing, resolving schema.rb inconsistency.

Other information

Migration is idempotent using column_exists? check to safely run on environments where the column may already exist.

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