monitor-test: add offline replay validation, white-screen detection flow, and reliability coverage gaps

[Copilot]

monitor-test was missing explicit validation paths for offline queue recovery and white-screen detection, and lacked a few practical reliability checks for parity with mature monitoring setups. This PR fills those gaps in the test portal with focused runtime hooks, UI controls, and documentation updates.

• Offline recovery validation (Error page)

  • Added queue introspection from reporter localStorage (key, itemCount, savedAt, sample event types).
  • Added explicit controls to:
    • emit offline probe events,
    • manually flush persisted queue,
    • refresh queue snapshot.
  • Wired online/offline listeners to auto-attempt flush on reconnect and log recovery signals in-page.

• White-screen detection validation (Error page)

  • Added reliability helpers with 18-point viewport sampling and container-hit ratio calculation.
  • Implemented thresholded detection loop (1s sampling, 6s sustained condition) and white-screen report path via reportError.
  • Added in-page simulation controls:
    • start/stop detector,
    • one-shot sampling,
    • 7s full-screen white mask trigger.
  • Added overlap guard to prevent concurrent async detection runs.

• Missing reliability signal in performance scenarios

  • Added performance_interaction_delay manual sample action (rAF-based interaction latency probe) on Performance page to complement INP-oriented regression checks.

• Runtime/build completeness

  • Added missing app/monitor-test/build/autoSourcemapUploadPlugin.ts referenced by Vite config, restoring monitor-test dev/build startup path.

• Docs and portal wording

  • Updated monitor-test/README.md route capability and acceptance guidance for:
    • offline queue recovery flow,
    • white-screen validation flow,
    • interaction-delay coverage.
  • Updated Home/Error page copy to reflect newly covered capabilities.

// white-screen detector core (simplified)
const snapshot = collectWhiteScreenSnapshot(['#root', '.portal-shell'], ['.skeleton', '.loading', '[data-skeleton]'])
if (snapshot.ratio >= 0.95 && sustainedForMs >= 6000) {
  await reportError('white_screen', {
    message: 'Potential white screen detected in monitor-test',
    detail: { sample: snapshot, duration: sustainedForMs },
  })
}

Original prompt

test项目中我的离线重新恢复上传好像没有在里面，还有白屏检测也没有，帮我仔细去补充完善test项目，同时还要帮我看看有什么功能欠缺或者指标没有监控到的帮我搞好（去网上找优秀的开源监控系统去对标）

The user has attached the following file paths as relevant context:

• .github\copilot-instructions.md

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