Lines 8 and 22 of digest.mjml hardcoded #7161FF for the event-item
border-left and footer link color, while mailer.ts already passes
brandAccent into the template (used at lines 15 and 34). When
BRAND_ACCENT is customized, the border and footer links stayed the
default purple.
Drive both from {{brandAccent}} so they respect the customization.
Fixes bead mailship-hu5
