fix(example): make web layouts resize safely and preserve list modes

[OskarEichler]

Fixes

Replace module-scope window access with reactive window dimensions, remount the layout-options list when orientation changes and make mode buttons select rather than toggle. Bound ComplexMasonry pagination timers and use the exported FlashList in the web grid.

Compatibility / observable changes

Example-only changes. Importing these examples without window no longer throws; viewport changes update height. Orientation controls remount as required by FlashList. No library API change.

Verification

• Consumer verification: the combined fixes were packaged on the unchanged npm 2.3.2 runtime baseline and checked with React Native 0.87.1 / React 19.2.3. Immutable install, lint, both Android Debug variants, both unsigned iOS Simulator variants, four Metro bundles, 13 web targets and four browser-extension builds pass. All 298 installed non-metadata package files match the reviewed artifact byte-for-byte.
• Independent patch applied to 435b5141df4960ebbbc0b93264db3f5a4b23fffd: all 187 existing tests (14 suites), library TypeScript build and changed-file ESLint pass.
• One-off actual-source regression diagnostics pass:
  • fixture/react-native/src/Grid renders without window and follows viewport height
  • fixture/web/Grid renders without window and follows viewport height
  • fixture/react-native/src/Masonry renders without window and follows viewport height
  • fixture/react-native/src/ComplexMasonry renders without window and follows viewport height
  • fixture/react-native/src/LayoutOptions renders without window and follows viewport height
  • fixture/react-native/src/DynamicColumnSpan renders without window and follows viewport height
  • layout options remounts when changing orientation
  • dynamic column controls select rather than toggle their mode
  • masonry pagination duplicate
  • masonry pagination unmount
• The combined review workspace passes Android Debug, unsigned iOS Simulator Debug/Release, both production Metro bundles, web production export, Docusaurus/Jekyll builds and all 24 existing iOS Detox tests (10 suites). The contacts comparison was rerun after its final change. These combined-workspace results are not a claim that every device/platform was tested independently for this PR.
• No checked-in tests, reference screenshots, dependency versions or native SDK versions were changed.

Reviewers’ hat-rack 🎩

• Check the stated compatibility behavior and reproduce the relevant cases above.
• Run the existing test/type/lint commands and exercise the affected example or list behavior on your supported device matrix.

Physical-device behavior, Android Detox, assistive-technology conformance and release signing were not verified. No app deployment is part of this PR.

[OskarEichler]

I have signed the CLA!