FCE-3336: Emit error if react-native-get-random-values is missing

[MiloszFilimowski]

Description

• Add assertReactNativeWebrtcNativeModule check that verifies NativeModules.WebRTCModule is linked and throws an actionable error with install/rebuild steps when missing.
• Add assertGetRandomValuesPolyfill check that verifies globalThis.crypto.getRandomValues works and throws an actionable error pointing to react-native-get-random-values when missing.
• Run both assertions after registerGlobalsPolyfill() in packages/mobile-client/src/webrtc-polyfill.ts.

Motivation and Context

Surface a clear, actionable error at startup when required native dependencies are missing or not linked, instead of letting the SDK fail later with cryptic runtime errors.

Documentation impact

• Documentation update required
• Documentation updated in another PR
• No documentation update required

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)

[linear]

FCE-3336

[Copilot]

Pull request overview

This PR adds early startup assertions in the React Native client to surface actionable errors when required native dependencies (WebRTC native module and crypto.getRandomValues polyfill) are missing or not linked, avoiding later/cryptic runtime failures.

Changes:

• Added a runtime assertion to verify NativeModules.WebRTCModule is present and throw an install/rebuild guidance error if not.
• Added a runtime assertion to verify globalThis.crypto.getRandomValues is functional and throw an error pointing to react-native-get-random-values if not.
• Invoked both assertions immediately after the existing registerGlobalsPolyfill() initialization.

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