fix(remix): correct component accessibility and bounded layout

[leoafarias]

Summary

• give NakedButton the visible button label when no explicit semantic label is supplied
• constrain callout text and custom content with a loose flex fit so bounded callouts wrap without forcing intrinsic content to fill the row
• use the opaque accent text step for non-solid Fortal badges and verify WCAG AA contrast across every supported accent and both brightness modes
• apply Fortal text-field foreground colors through textColor, keeping editable text styling separate from container decoration

Why

The Muse Studio integration exposed four generic Remix behaviors that had diverged on a retired feature branch. This PR fixes the underlying component contracts in the canonical Remix source instead of preserving a second vendored implementation.

Validation

• focused regression suite: 133 tests passed
• fvm dart analyze packages/remix
• fvm dart run melos run ci --no-select
  • generated sources unchanged
  • demo: 15 tests passed
  • remix: 1,889 tests passed