Add split-track slider support and expand VT coverage

[han4wluc]

Summary

• add optional inactiveBarSrc support so sliders can render split active and inactive track textures while keeping the single-track mode fully supported
• fix VT/manual rendering reliability by explicitly presenting RouteGraphics frames and by tightening VT template state parsing and optional media loading
• add visible split-track slider fixtures and expand slider VT coverage across horizontal and vertical, single-track and split-track, and hover and no-hover combinations
• bump the package patch version to 1.1.6

Testing

• bun run test
• bun run vt:screenshot