feat: make stop icon and loading cursor customizable via CSS variables

[nzjrs]

Replace hardcoded SVG/Tailwind with CSS mask-image rendering so the shape, color, size, and animation of the stop icon and loading cursor can be overridden via theme.json or custom CSS.

CSS variables exposed:

--stop-icon-mask SVG data URI for icon shape
--stop-icon-color defaults to currentColor
--stop-icon-animation defaults to none

--loading-cursor-mask SVG data URI (omit for default circle)
--loading-cursor-color defaults to hsl(var(--foreground))
--loading-cursor-size defaults to 0.875rem
--loading-cursor-animation defaults to pulse

Simple example (breathing pulse on both):

  :root {
      --stop-icon-animation: my-pulse 2s ease-in-out infinite;
      --loading-cursor-animation: my-breathe 2s ease-in-out infinite;
      --loading-cursor-size: 1.25rem;
  }
  @keyframes my-pulse {
      0%, 100% { opacity: 1; transform: scale(1); }
      50% { opacity: 0.5; transform: scale(0.92); }
  }
  @keyframes my-breathe {
      0%, 100% { opacity: 1; transform: scale(1); }
      50% { opacity: 0.35; transform: scale(0.85); }
  }

Advanced example (custom icon shape and color):

  :root {
      --stop-icon-animation: stop-pulse 0.8s ease-in-out infinite;
      --loading-cursor-mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='24' height='24' viewBox='0 0 24 24'%3E%3Cpath d='M9 18l6-6-6-6' stroke='white' stroke-width='2.5' stroke-linecap='round' stroke-linejoin='round' fill='none'/%3E%3C/svg%3E");
      --loading-cursor-color: hsl(120, 60%, 55%);
      --loading-cursor-animation: chevron-spin 0.9s linear infinite;
  }
  @keyframes stop-pulse {
      0%, 100% { opacity: 1; transform: scale(1); }
      50% { opacity: 0.2; transform: scale(1.35); }
  }
  @keyframes chevron-spin {
      from { transform: rotate(0deg); }
      to { transform: rotate(360deg); }
  }

[cubic-dev-ai]

No issues found across 3 files

[hayescode]

Reviewed via Codex

LGTM.

ci failing

[hayescode]

@nzjrs please fix CI then we're good to merge!