Add Authier to the OSS Directory

[capaj]

Summary

• add Authier as the authier-pm project, following the dedicated GitHub organization naming rule
• register its canonical website, GitHub organization, and public social profile
• describe the password manager's client-side encrypted sync and trusted-device approval

I maintain Authier and am submitting this project with that affiliation disclosed.

Validation

• pnpm run validate
• pnpm lint
• git diff --check