De-couple the web handlers from React Native (#4381)

## Description

Removes the last react-native dependency from `src/web`:

- `NativeViewGestureHandler` used `Platform.OS !== 'web'` to guard its
DOM-touching `init()` logic from react-native-windows. The guard is now
`!canUseDOM() || !(view instanceof Element)` — `canUseDOM()` is a new
engine-local duplicate of the `useIsomorphicLayoutEffect` check
(checking `window` alone isn't enough, RN defines it on every platform),
and `Element` covers SVG-backed views, replacing the `as HTMLElement`
cast with real narrowing.
- Five timeout fields in the Pan/LongPress/Tap handlers become
`ReturnType<typeof setTimeout> | undefined` — `number` breaks
compilation for consumers with `@types/node` in their TS program. Pan's
`= 0` sentinels are dropped (`clearTimeout(undefined)` is the same
no-op).
- New lint rule: no react-native imports in `src/web/**`.

## Test plan

- `yarn ts-check` clean; `yarn test` 103/103; `yarn lint:js` 0 errors;
lint rule verified firing
- Verified on react-native-web (expo-example web in Safari): rendering +
native-button role detection through the new guard; LongPress activation
(the retyped timeout firing); Pan drag incl. the finalize path that
clears the never-assigned timeout — the one runtime-visible change