Add error notification system with alert dialogs and stack trace logging

[Copilot]

Implements centralized error handling: all system errors now display via alert() with full stack traces logged to console. Only runScenario() catches errors; all other handlers throw exceptions for proper propagation.

Changes

Logger enhancement (src/utils/logger.ts)

• Added logError() function capturing stack traces via stacktrace-js
• Null-safe stack frame property access with fallback logging

Error handling unification (src/core/index.js)

• runScenario(): wrapped in try-catch, logs errors and shows alert dialog
• Resource handlers (getImageObject, getSoundObject, executeCode, loadHandler): removed silent error handling, now throw exceptions
• Removed duplicate checkResourceExists() method

Error flow:

// Handler throws exception
async getImageObject(line) {
  if (!(await this.checkResourceExists(line.src))) {
    throw new Error(`Image file not found: ${line.src}`)
  }
  // ...
}

// runScenario catches, logs, and alerts
async runScenario() {
  try {
    await boundFunction(scenarioObject)
  } catch (error) {
    await logError(error, 'Error in runScenario')  // Console: full stack trace
    alert(`システムエラーが発生しました:\n${error.message}`)  // User: clear message
  }
}

Console output example:

ERROR:
Context: Error in runScenario
Message: Image file not found: /src/resource/image.png
Stack trace:
    at getImageObject (index.js:481:7)
    at showHandler (index.js:384:26)
    at runScenario (index.js:229:13)

Test coverage: 6 unit tests for logger functionality in tests/logger.test.ts

Original prompt

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This section details on the original issue you should resolve

<issue_title>エラー表示の追加</issue_title>
<issue_description>システムエラーを、Alertで通知し、エラーログにスタックトレースを保存する

runScenario以外は、例外をスローする。

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Trelloから移行 (todo): https://trello.com/c/CYhKe2cZ</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes エラー表示の追加 #85

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