fix(Drawer): prevent nested drawer mask stacking

[epolikrati]

Problem

When multiple <Drawer> components are open simultaneously (e.g. opening a drawer from within another drawer), each instance independently renders its own semi-transparent backdrop mask. The masks stack on top of each other, causing the background to become progressively darker with each additional drawer. Navigating back and forth compounds the issue that the accumulated backdrop layers are never cleaned up, making the left side of the screen increasingly opaque.

Changes

• New useDrawerStackPosition hook: Maintains a module-level openDrawerStack array tracking all open drawer instances by useId(). Uses useSyncExternalStore for tear-free reads and useLayoutEffect for synchronous registration/cleanup. Only the drawer at index 0 (the first opened) returns isBottomMostOpenDrawer: true — all subsequent drawers render a transparent mask instead.
• Removed showMask prop from DrawerProps: Mask visibility is now fully automatic based on stack position — consumers no longer need to pass showMask. The Mask component accepts visible (controls background opacity) and onClick (optional close handler) instead of the previous onClose.
• Conditional mask rendering and click behaviour: shouldRenderMask = closeOnOutsideClick || isBottomMostOpenDrawer ensures the mask element exists when needed for click interception or backdrop display. shouldShowVisibleMask = isBottomMostOpenDrawer controls whether the backdrop is opaque or transparent. When closeOnOutsideClick is false, the mask renders (visible if bottom-most) but doesn't fire the close callback.
• maskContainer style converted to function: Now accepts a visible boolean — renders rgba(0, 0, 0, 0.45) when visible, transparent otherwise. Added data-mask-visible attribute for test assertions.
• Extracted DRAWER_ROOT_ID constant from inline string to constants.ts.
• 102-line hook test suite (useDrawerStackPosition.test.ts): Covers single drawer, nested drawers, 3-deep nesting, closing top/bottom drawer promotion, and unmount while open.
• 84 lines of new integration tests in Drawer.test.tsx: Covers visible mask with closeOnOutsideClick=false, disabled outside click, single visible mask with multiple drawers, and mask promotion on close.

Fixes

• Multiple backdrop overlays stacking when opening nested drawers — now only the bottom-most drawer shows the visible mask.
• Backdrop darkening on repeated back-and-forth navigation — stack cleanup happens synchronously on close/unmount.

[xanderantoniadis]

Solid solution! good job 👏

[github-actions]

🎉 This PR is included in version 6.7.6 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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