fix(web): start at 0 when value is 0 and the range includes 0

[huytdps13400]

Summary:

Fixes #828

On web, <Slider minimumValue={-8} maximumValue={8} value={0} /> renders the thumb at the minimum instead of in the middle.

Root cause: RNCSliderNativeComponent.web.tsx seeds its state with initialValue || minimumValue. 0 is falsy, so it falls back to minimumValue. The layout effect never corrects it, because lastInitialValue also starts at 0. Note that Slider forwards value={0} as undefined (passedValue), so the web component can't tell "no value" apart from value={0}. Because of that, the ?? approach suggested in the issue wouldn't fix it on its own.

Change: fall back to minimumValue only when 0 lies outside [minimumValue, maximumValue]. When the range includes 0, the initial value is 0, which matches the documented default and the currentValue that Slider already uses for step markers. Nothing else changes: non-zero values work as before, ranges where 0 is below the minimum still start at minimumValue, and the effect guard for uncontrolled sliders is untouched.

Test Plan:

Added package/__test__/RNCSliderNativeComponent.web.test.tsx. It renders the web component, fires responderGrant, and checks the value passed to onRNCSliderSlidingStart and the minimum track's flexGrow (the thumb position as a percentage).

• Before the fix: 2 of the 4 new tests fail (value={0} and no value with range -8...8 report -8 instead of 0).
• After the fix: all pass. npx eslint src __test__ reports 0 errors (same warnings as main), and npx tsc --noEmit passes.

Note: npx jest currently fails on main for every suite (this._moduleMocker.clearMocksOnScope is not a function). The react-native jest preset's environment resolves jest-environment-node@29 against jest@30, and CI shows the same failure. I ran the suite locally with a jest 30 node environment (--testEnvironment pointing at a copy of react-native/jest/react-native-env.js that extends jest-environment-node@30): 5 suites / 20 tests pass. This PR doesn't change the jest setup.

This fix was prepared with AI assistance (Claude Code) and verified locally with the tests above.

🤖 Generated with Claude Code