## Summary
This PR fixes account deletion failures by changing how orphaned user
emails are rewritten during `AccountDeletionService`.
Ref:
https://chatwoot-p3.sentry.io/issues/6715254765/events/e228a5d045ad47348d6c32448bc33b7a/
## Changes (develop -> this branch)
- Updated soft-delete email rewrite from:
- `#{original_email}-deleted.com`
- To deterministic value:
- `#{user.id}@chatwoot-deleted.invalid`
- Added reserved non-deliverable domain constant:
- `@chatwoot-deleted.invalid`
- Replaced the "other accounts" check from `count.zero?` to `exists?`
(same behavior, cheaper query).
- Updated service spec expectation to match deterministic email value
and assert it differs from original email.
## Files changed
- `app/services/account_deletion_service.rb`
- `spec/services/account_deletion_service_spec.rb`
## How to verify
- Run: `bundle exec rspec
spec/services/account_deletion_service_spec.rb`
- Run: `bundle exec rubocop app/services/account_deletion_service.rb
spec/services/account_deletion_service_spec.rb`
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