fix: macOS Designed for iPhone — liquid glass background + mouse drag support

[isaacrowntree]

Summary

Two fixes for macOS "Designed for iPhone/iPad" compatibility mode (Apple Silicon):

1. Liquid glass background

sheet.backgroundEffect with UIColorEffect is silently ignored by the macOS compatibility layer. This causes the default iOS 26 liquid glass material to show through instead of the configured backgroundColor. The same binary works correctly on real iOS devices (tested iPhone 17 Pro, iOS 26.2).

Fix: Remove the early return when NSProcessInfo.processInfo.isiOSAppOnMac is YES, so view.backgroundColor is also set as a fallback alongside backgroundEffect.

2. Mouse drag gestures

UISheetPresentationController's built-in pan gesture doesn't respond to mouse/trackpad input on Mac. Users can only interact with the sheet by tapping the grabber.

Fix: Add a custom UIPanGestureRecognizer on the presentedView (guarded by isiOSAppOnMac) that computes a projected landing position on release using the drag's cumulative translation + velocity (decelerating over ~0.3s), then snaps to the nearest detent. This mimics native iOS release-to-snap behavior.

• Gesture covers the header/grabber area — scroll view content remains scrollable at any detent
• Uses resolvedHeightForIndex: (now exposed in TrueSheetDetentCalculator.h) for accurate detent position calculations
• No mid-drag snapping = no jitter
• Both fixes are gated behind NSProcessInfo.processInfo.isiOSAppOnMac (iOS 14+) — zero change on real iOS devices

Test plan

• Run on macOS "Designed for iPhone/iPad" — sheet has solid backgroundColor, no liquid glass
• Run on macOS — drag header/grabber area up/down with mouse, release to snap to nearest detent
• Run on macOS — fast flick up/down snaps in the flick direction
• Run on macOS — scroll view content scrolls normally at all detents
• Run on physical iOS device (iOS 26+) — sheet background and drag unchanged
• Run on iOS Simulator — no regression
• Test with backgroundColor set
• Test with backgroundBlur set (no backgroundColor)
• Test with dismissible={false} and dismissible={true}

Reproduction app: https://github.com/isaacrowntree/truesheet-macos-liquid-glass-repro

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[github-actions]

Hey @isaacrowntree, this PR is missing a changelog entry.

Add the following under the Unreleased section in CHANGELOG.md:

- **platform**: Description. ([#598](https://github.com/lodev09/react-native-true-sheet/pull/598) by [@isaacrowntree](https://github.com/isaacrowntree))

See CONTRIBUTING.md for more details.