Microservice to bring 2FA to self hosted PDSes

feat(gatekeeper): parameterize 2fa email template branding and URLs #55

targeting main from spotchi.eurosky.social/pds-gatekeeper:spotchi/brand-parameters
Open opened by and assigned to spotchi.eurosky.social
targeting main from spotchi.eurosky.social/pds-gatekeeper:spotchi/brand-parameters

This change makes the gatekeeper 2FA email template configurable instead of hardcoding Bluesky branding.

It adds environment-driven branding fields for the 2FA email subject, brand name, tagline, logo, home link, settings link, and footer mark, then passes those values into the Handlebars template.

Commits 1

feat(gatekeeper): parameterize 2fa email template branding and URLs