Add regression test for dir attribute preservation in email sanitizer

[Copilot]

This addresses the PR review comment requesting coverage for the newly allowed dir attribute in EMAIL_SANITIZE_CONFIG. The change is scoped to a focused regression test to prevent future sanitizer regressions affecting RTL content.

• What changed

  • Added a unit test for sanitizeEmailHtml asserting that dir is preserved on sanitized elements (example: <p dir="rtl">...</p>).

• Why this matters

  • Ensures the sanitizer behavior matches the attribute allowlist update and protects RTL rendering support from accidental breakage.

• Example assertion

  expect(sanitizeEmailHtml('<p dir="rtl">مرحبا</p>'))
    .toContain('<p dir="rtl">مرحبا</p>');

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