[shossain786]

Closes #216

What & why

Adds a Copy failure details button to the expanded detail row of failed tests (Test Cases and Failures tabs). It copies the test id, error message and stack trace to the clipboard and shows "Copied" for 1.5s.

• Only rendered for FAILED tests that have an error message or stack trace.
• Uses navigator.clipboard when available, otherwise falls back to a hidden textarea + execCommand('copy'), so it works from file://.
• Reads text from the existing .error-msg / .stack-trace nodes, so the report doesn't grow; the test id is HTML-escaped in a data attribute.

Verification

• New HtmlReportGeneratorTest.copyFailureButton_onlyOnFailedTestsWithErrorDetail fails without the change and passes with it.
• Full mvn test: 870 tests, 0 failures.
• Generated a report and clicked the button in headless Chrome: both the clipboard-API path and the fallback copied Test: …\nError: …\n\n<stack trace>, and the label reverted after "Copied". Not checked: dark theme visually, a matrix run, or a real clipboard paste.

Type of change

• New feature (opt-in, report only)

Checklist

• Tests pass, new behaviour covered
• No new dependencies
• No changes to @SeleniumBootApi
• CHANGELOG.md updated

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