v0.2.0 of liquid_glass_native

Native Apple Liquid Glass UI for Flutter on iOS 26+ — real SwiftUI/UIKit glass widgets (buttons, tab bar, sheets, pickers), not a blur fake. Graceful fallback below iOS 26. Changelog excerpt: - Refactor: shared GlassPlatformViewbase class — fixes lifecycle bugs and reduces per-widget boilerplate. - New: brightnessproperty on LiquidGlassTabBarto control native interface style (light/dark). - Fix: theme-aware brightness on LiquidGlassSegmentedControl; invisible spinner on dark backgrounds is resolved.