Fix ReportingEndpoints URL validation causing CI test failure

[Copilot]

Description

The Build, test, and pack workflow failed because StartWithRelativeReportingEndpointUrlThrowsOptionsValidationException did not throw during options validation. This change tightens ReportingEndpoints URL validation to enforce absolute HTTP(S) URLs and adds focused regression coverage for non-HTTP schemes.

• Root cause

  • ValidateReportingEndpoints accepted URIs that should be rejected by policy intent, so invalid endpoint values bypassed startup validation.

• Validation logic update

  • Require successful absolute URI parsing.
  • Require http or https scheme for each ReportingEndpointOptions.Url.
  • Keep existing failure message contract unchanged.

• Regression coverage

  • Added NonHttpSchemeReportingEndpointUrlThrowsOptionsValidationException to assert file:///... is rejected.

else if (!Uri.TryCreate(endpoint.Url, UriKind.Absolute, out var uri))
{
    failures.Add($"{scope}: Reporting endpoint '{endpoint.Group}' URL must be absolute. Fix: use a full URL such as 'https://reports.example.com/csp'.");
}
else if (uri.Scheme != Uri.UriSchemeHttp && uri.Scheme != Uri.UriSchemeHttps)
{
    failures.Add($"{scope}: Reporting endpoint '{endpoint.Group}' URL must be absolute. Fix: use a full URL such as 'https://reports.example.com/csp'.");
}

Related Issue

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Checklist

• Code follows project coding standards
• Tests added/updated for changes
• All tests pass (dotnet test)
• XML documentation added for public APIs
• CHANGELOG.md updated