[a11y] Transactional email footer text doesn't have enough contrast

[jatinder14]

Issue Summary

Transactional emails (magic link, invites, password reset, comments, etc.) use footer/link color `#738A94` on white backgrounds. That is about 3.6:1, below WCAG 1.4.3 (4.5:1) for normal text.

Newsletter footers were updated to `#5B6B73` in #29670 / #29666. Transactional templates still hardcode `#738A94`.

Suggested fix

Replace `#738A94` with `#5B6B73` across transactional email templates (and matching snapshots).

Ghost Version

main

Code of Conduct

• I agree to be friendly and polite to people in this repository

[jatinder14]

Working on this — aligning transactional email footer greys with the newsletter contrast fix (#5B6B73).