AO3-7045 Migrate audits table to BIGINT

[alyssapowell]

Issue

https://otwarchive.atlassian.net/browse/AO3-7045

Purpose

Migrates the audits table primary key from integer to BIGINT to prevent integer overflow as the audit log grows. This is a preventive infrastructure improvement to handle the increasing volume of audit records in the system.

Testing Instructions

1. Run the migration in a development environment: rails db:migrate
2. Verify the schema change: Check that audits.id column is now BIGINT type
3. Test audit functionality: Ensure audit records are still created for tracked changes
4. Run existing test suite to verify no functionality breaks

References

This follows the same pattern as recent similar migrations:

• 20250704060231_change_bookmark_foreign_keys_type.rb
• 20250718220533_change_subscriptions_id_to_bigint.rb

Credit

Alyssa Powell (she/her)

[Bilka2]

The migration in this PR needs to be updated to be have a timestamp after 12 November 2025, as defined in the schema file:

otwarchive/db/schema.rb

Line 13 in 1c45632

ActiveRecord::Schema[7.2].define(version: 2025_11_12_114418) do

Please note that we may take over the code in this PR (with credit) because we are hoping to finish the bigint migrations soon and this PR has been stalled for a few months now.

[brianjaustin]

Adopted in #5516