## Description
Modified the phone number validation in Whatsapp::ChannelCreationService
to check for duplicate phone numbers across ALL accounts, not just
within the current account.
## Type of change
- [ ] Bug fix (non-breaking change which fixes an issue)
## How Has This Been Tested?
- Added test coverage for cross-account phone number validation
- Using actual UI flow
<img width="1493" height="532" alt="image"
src="https://github.com/user-attachments/assets/67d2bb99-2eb9-4115-8d56-449e4785e0d8"
/>
## Checklist:
- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules
90352b3a20