Center Fader thumbs in both orientations

[0thernet]

What changed

• center Fader thumbs on the cross axis for horizontal and vertical orientations
• add both orientations to the public gallery
• verify rendered thumb-to-track geometry at compact and wide browser layouts
• prepare the immutable v0.1.5 release metadata and generated distribution

Root cause

React Aria supplies the thumb coordinate only on the value axis. The shared Fader CSS did not define the cross-axis coordinate, so horizontal thumbs floated above their tracks and vertical thumbs could drift sideways.

Validation

• bun run check
• 101 tests, 0 failures, 103,335 assertions
• React 18 and React 19 installed-package smoke tests
• compact and wide browser geometry gates
• bun pm pack --dry-run --ignore-scripts
• Node 24 imports of all generated entries
• git diff --check