Copy update: American Express card support

[machikoyasuda]

Update copy across the user-facing flow and the Help page to include American Express as an accepted bank card.

Figma: See changes ready for dev here - https://www.figma.com/design/SeSd3LaLd6WkbEYhmtKpO3/branch/nXet3uhOBu3bhgTudKQx8e/Benefits-(Full-Application)?ready-for-dev=1&m=dev

Status: Blocked b/c Littlepay doesn't accept AmEx yet.

Acceptance Criteria

• Update all English copy
• Update all Spanish copy, ask @lalver1 for help/testing

Where the copy is

• Help page
• Eligibility start
• Contactless modal
• Enrollment index
• CalFresh alert

Additional context

We are not changing these things at this time:

• "issued by" versus "by": Inconsistency is acknowledged but not part of this ticket's scope.
• not getting this professionally translated by our contractor
• not necessarily changing the way we deliver copy

This PR needs to be merged when we are cleared to do so by Product, after Littlepay's AmEx compatibility begins.