Add small FAB, range slider, three-line list item

[jserv]

This introduces new MD3 widgets to improve component coverage:

• 40dp small FAB variant per MD3 spec (12dp corner radius, 24dp icon). Also fix touch target handling in iui_fab_internal to expand hit area to 48dp minimum for all FAB variants, ensuring MD3 accessibility compliance.
• Two-thumb range slider for selecting value ranges. Features distance-based thumb selection when target overlap, per-thumb crossing resolution after step quantization, and division-by-zero guards for both the new range slider and the existing single-thumb slider.
• Convenience wrapper for 88dp three-line list items with overline, headline, and supporting text, mirroring the existing iui_list_item_two_line pattern.

---

Summary by cubic

Adds MD3 small FAB, a two-thumb range slider, and a three-line list item to broaden widget coverage. Improves FAB accessibility and hardens slider math for stability.

• New Features

  • Small FAB (40dp, 12dp radius, 24dp icon).
  • Range slider for selecting a value range with smart thumb selection and crossing handling.
  • Three-line list item (overline, headline, supporting) with optional leading icon.

• Bug Fixes

  • Expand FAB touch targets to a 48dp minimum across variants.
  • Add division-by-zero guards to slider calculations.

^{Written for commit d0953ca. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 6 files