background blur changes + examples

[MiloszFilimowski]

Description

Background blur in the fishjam-chat example, plus the react-client fixes it needs:

1. Re-apply the camera middleware to new device tracks (react-client). A middleware set before the camera started was never applied, and a camera switch published the raw track for a moment. Now every new device track goes through the middleware before it is published, and a middleware that finishes setting up after it was replaced releases itself.
2. Release the previous middleware only after the published track is swapped (react-client). Switching blur off used to release the blurred track first and swap it out of the published stream second. On React Native, releasing disposes the track natively, so the swap could no longer remove it: the dead track stayed in the stream and the local tile froze on every toggle (Android). applyMiddleware now builds the new track, publishes it through a callback from the caller, and releases the old one last. The latest request wins: one that is replaced while it sets up releases itself.
3. Background blur in fishjam-chat (example). A blur button on the preview and room screens hands a middleware from @fishjam-cloud/video-effects to useCamera().setCameraTrackMiddleware. No provider, no custom source:

export const backgroundBlur = createCameraEffectMiddleware(
  createBackgroundBlurEffect(() => ({ segmentation, radius: 24 })),
);

const { currentCameraMiddleware, setCameraTrackMiddleware } = useCamera();
const isBlurOn = currentCameraMiddleware === backgroundBlur;
setCameraTrackMiddleware(isBlurOn ? null : backgroundBlur);

The model is read through expo-asset and expo-file-system, because an Android release build cannot fetch a bundled asset. The example moves to Expo SDK 57 / React Native 0.86.3, which react-native-worklets 0.12 requires, and sets iphoneDeploymentTarget: "16.4" in its Fishjam plugin options because Expo SDK 57 pods need it. The plugin default stays 15.1.

Motivation and Context

Camera effects on Fishjam's own camera track, shown in the example with the smallest possible app code. The react-client fixes came out of testing it on devices.

Uses @fishjam-cloud/video-effects 0.1.3 (fishjam-cloud/video-effects#4), which adds createCameraEffectMiddleware.

Related fork fix, released in @fishjam-cloud/react-native-webrtc 0.30.4 and not required by this PR: fishjam-cloud/fishjam-react-native-webrtc#91 (a released track leaves every local stream).

Checked

• react-client unit tests: 77 pass; cameraMiddleware.spec.ts covers cold start, camera off and on, replacement and clearing while pending, onClear running once, and the previous middleware being released after replaceTrack.
• Galaxy S23, debug and release builds: blur on and off on the preview and in the room, published tile blurred, room tile stays live across toggles.
• iPhone: same on the preview and in the room.
• Two phones in one room: each side's blur shows on the other phone.

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)

https://claude.ai/code/session_01MUzB8Nef5pJqJMBoPHgJNJ