FCE-2777: Add data channels example on mobile

[MiloszFilimowski]

Description

• Reexports useDataChannel
• Data Channel example (web clone)

Motivation and Context

• New data channels api was not exported on mobile

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-2777 Add data channels example on mobile

[Copilot]

Pull request overview

This PR exposes the new data channels hook from the mobile SDK and adds a new Expo React Native “text chat” example demonstrating data-channel usage (ported from the web example).

Changes:

• Re-export useDataChannel and UseDataChannelResult from @fishjam-cloud/react-native-client.
• Add a new examples/mobile-client/text-chat Expo app showing a basic chat over data channels.
• Update workspace lockfile to include the new example workspace.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
yarn.lock	Adds the new mobile-text-chat workspace entry and dependencies.
packages/mobile-client/src/index.ts	Re-exports useDataChannel and UseDataChannelResult from the underlying react-client package.
examples/mobile-client/text-chat/tsconfig.json	Adds strict TypeScript config for the new example app.
examples/mobile-client/text-chat/screens/home/index.tsx	Home screen UI for entering room/user and connecting.
examples/mobile-client/text-chat/screens/chat/index.tsx	Chat UI using useConnection + useDataChannel to send/receive messages.
examples/mobile-client/text-chat/prettier.config.js	Adds Prettier config hook-up for the example.
examples/mobile-client/text-chat/package.json	Declares the new example workspace and Expo dependencies.
examples/mobile-client/text-chat/navigation/RootNavigation.tsx	Stack navigation between Home and Chat screens.
examples/mobile-client/text-chat/index.ts	Expo root registration.
examples/mobile-client/text-chat/hooks/useConnectFishjam.ts	Encapsulates sandbox token fetching + joinRoom + navigation.
examples/mobile-client/text-chat/eslint.config.js	Adds ESLint config hook-up for the example.
examples/mobile-client/text-chat/assets/README.md	Notes asset reuse from another example.
examples/mobile-client/text-chat/app.json	Expo app configuration (icons, bundle IDs, plugin).
examples/mobile-client/text-chat/App.tsx	Wraps app with FishjamProvider, navigation, and safe area provider.
examples/mobile-client/text-chat/.gitignore	Ignores common Expo/RN build artifacts and env files.
examples/mobile-client/text-chat/.env.example	Documents required EXPO_PUBLIC_FISHJAM_ID.

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