[FCE-3631] Documentation for VoIP feature

[Magmusacy]

Description

Adds a how-to guide for the React Native SDK's VoIP feature: docs/how-to/client/voip-calls.mdx.

The page covers the full app side: native setup (Expo / Bare tabs), the VoipProvider contract (join the room on connecting, reportConnected() when media is live), incoming push payload, outgoing calls, ending calls and lastEndedReason, hold/mute, and Recents redial. All snippets type-check against the bumped web-client-sdk submodule.

Supporting changes: sidebar positions + a cross-link from Background streaming, a twoslash error-handling tweak in docusaurus.config.ts, spelling entries, submodule bumps.

Note: links to the voip-call example 404 until the SDK-side PR merges.

[linear]

FCE-3631

[Copilot]

Pull request overview

Adds a new “VoIP calls” how-to guide for the React Native (mobile) SDK, covering PushKit/APNs on iOS and FCM/Telecom on Android, and updates navigation/supporting docs to incorporate the new page.

Changes:

• Introduces a comprehensive VoIP calls guide under docs/how-to/client/.
• Adjusts sidebar ordering (sidebar_position) across nearby client how-to pages to make room for the new guide.
• Updates spellchecker allowlist to include VoIP/CallKit/PushKit/Telecom/APNs/FCM and related terms.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
spelling.txt	Adds VoIP-related proper nouns/terms to the spellchecker allowlist.
docusaurus.config.ts	Tweaks Shiki/Twoslash error filtering helper used during MDX rendering.
docs/how-to/client/voip-calls.mdx	New VoIP calls documentation page for React Native apps (iOS/Android).
docs/how-to/client/text-chat.mdx	Updates sidebar ordering to accommodate the new VoIP page.
docs/how-to/client/simulcast.mdx	Updates sidebar ordering to accommodate the new VoIP page.
docs/how-to/client/migration-guide.mdx	Updates sidebar ordering to accommodate the new VoIP page.
docs/how-to/client/ios-simulator-camera.mdx	Updates sidebar ordering to accommodate the new VoIP page.
docs/how-to/client/background-streaming.mdx	Adds a “See also” link pointing readers to the new VoIP calls guide.

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