feat: release-react-sdk-v4 (#1238)

This PR will release the v4 major version of React SDK.

We should not merge this in until we have our docs ready.

SDK-1568

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Docs/metadata/release-config changes only; no runtime code paths are
modified.
> 
> **Overview**
> Prepares the `@launchdarkly/react-sdk` package for its v4 major
release by updating release automation and SDK metadata.
> 
> This sets `packages/sdk/react` to `release-as: 4.0.0` in
`release-please-config.json`, adds `inlineContextCustomEvents` to the
React SDK’s feature list in `.sdk_metadata.json`, refreshes
`packages/sdk/react/README.md` to point at the main docs and include
SLSA provenance guidance, and removes the temporary
`temp_docs/MIGRATING.md` document.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
cdd54bf. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: joker23

.sdk_metadata.json

@@ -186,6 +186,7 @@
         "experimentation": { "introduced": "2.9" },
         "flagChanges": { "introduced": "2.9" },
         "hooks": { "introduced": "3.7" },
+        "inlineContextCustomEvents": { "introduced": "4.0" },
         "perContextSummaryEvents": { "introduced": "3.8" },
         "pluginSupport": { "introduced": "3.7" },
         "privateAttrs": { "introduced": "2.9" },

packages/sdk/react/README.md

@@ -6,18 +6,13 @@
 [![NPM][react-sdk-dm-badge]][react-sdk-npm-link]
 [![NPM][react-sdk-dt-badge]][react-sdk-npm-link]
 
-⚠️⚠️⚠️
+## Getting started
 
-> [!CAUTION]
-> This SDK is in pre-release and not subject to backwards compatibility 
-> guarantees. The API may change based on feedback.
->
-> Pin to a specific minor version and review the [changelog](./CHANGELOG.md) before upgrading.
+Refer to the [SDK documentation](https://launchdarkly.com/docs/sdk/client-side/react/react-web) for instructions on getting started with using the SDK.
 
-☝️☝️☝️
+## Verifying SDK build provenance with the SLSA framework
 
-## Getting started
-Refer to the [SDK documentation](https://launchdarkly.com/docs/sdk/client-side/react/react-web#get-started) for instructions on getting started with using the SDK.
+LaunchDarkly uses the [SLSA framework](https://slsa.dev/spec/v1.0/about) (Supply-chain Levels for Software Artifacts) to help developers make their supply chain more secure by ensuring the authenticity and build integrity of our published SDK packages. To learn more, see the [provenance guide](../../../PROVENANCE.md).
 
 ## About LaunchDarkly