feat(live-preview): expose preview status helper [SPA-5289]

[Maxim Cheremisin (maxcheremisin)]

Summary

Expose Preview Session transport status to the containing preview host and wire it into the React, Svelte, and Angular live-preview adapters.

Description

The shared live-preview client exposes subscribeStatus. The exported sendPreviewStatus helper publishes this message:

{
  source: 'experiences/live-preview',
  type: 'status',
  status: 'live' | 'static',
}

Each raw live-preview adapter subscribes to the shared client status:

• packages/adapter-react/src/use-live-preview-experience.ts
• packages/adapter-svelte/src/use-live-preview-experience.svelte.ts
• packages/adapter-angular/src/inject-live-preview-experience.ts

The combined hooks inherit the behavior through their raw-data hooks. Adapters send static when Preview Session options are absent or incomplete, live after the WebSocket opens, and keep live during reconnects. Status subscriptions are cleaned up with the data subscriptions.

The generic package owns the message format and transport status. The framework adapters only connect that status to the host-message helper.

This PR is stacked on #165 (feat/SPA-5161-live-preview-adapters).

Motivation and Context

The containing preview host needs to know whether the SDK is using static preview updates or an active Preview Session connection. A shared helper keeps this protocol consistent across direct package users and all framework adapters.

Validation

• npx nx test live-preview
• npx nx test adapter-react
• npx nx test adapter-svelte
• npx nx test adapter-angular
• npm ci --dry-run --ignore-scripts --no-audit --no-fund

PR Checklist

• I have read the CONTRIBUTING.md file
• All commits follow conventional commits
• Documentation is updated (if necessary)
• PR doesn't contain any sensitive information
• There are no breaking changes

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