docs: mark React Native autocapture as experimental (beta)

[rahul-mixpanel]

Why

React Native developers never see the native SDKs' documentation, so autocapture's beta status was invisible on this side. This mirrors mixpanel-android#999 and mixpanel-swift#768, with the same wording.

Stacked on #452 — merges into feat/autocapture-sample-el-id-screens.

What changed

• @experimental JSDoc on the autocapture typings in index.d.ts: AutocaptureOptions and its three sub-interfaces, ClickEventData, the Autocapture class, and Mixpanel#autocapture
• the same note on the Autocapture class and the autocapture getter in index.js, so it appears in editor hovers for JavaScript consumers too
• a short callout near the top of the README

No runtime warning is added here on purpose: enabling autocapture goes through the native SDKs, which already log one when it starts, so emitting from JS as well would print it twice.

Documentation only — no API or behaviour change.

One gap this PR does not close

index.js:902 still maps clickEvent.accessibleLabel onto $attr-aria-label for manual trackClick calls, and ClickEventData.accessibleLabel is still in the typings. Both native SDKs stopped capturing and reporting that property (mixpanel-android#997, mixpanel-swift#767) because accessibility labels are localized and can carry user data — so the JS wrapper can currently reintroduce, by hand, the exact property that was deliberately removed.

Fixing it means removing accessibleLabel from ClickEventData and the property mapping, which is a JS API change and belongs with the label-removal work rather than a docs PR. Happy to open it as a follow-up.

Testing

The package's jest suite is unchanged: 298 passing, with the same 8 pre-existing failures before and after — verified by stashing these changes and re-running.

🤖 Generated with Claude Code

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

The changes are documentation-only, consistently describe autocapture as beta, and do not alter runtime behavior or public type signatures.

Important Files Changed

Filename	Overview
README.md	Adds a prominent, accurate beta-status callout for autocapture.
index.d.ts	Adds consistent experimental annotations to autocapture typings and the Mixpanel accessor.
index.js	Adds matching experimental JSDoc to the autocapture class and getter without runtime changes.

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