Add 'Email me' action to send quiz results via mailto

[Rtavare]

Motivation

• Allow participants to send themselves their quiz result via their device's mail client so they can keep or share the outcome outside the browser.

Description

• Added an Email me button to the result action row in the results view and wired it into the UI markup (index.html).
• Added i18n strings for the email button and subject in both English and Spanish (btn_email, email_subject) and an email validation alert string (alert_email_invalid), and updated applyStaticTranslations() to set the button label.
• Implemented emailResult() which builds a mailto: URL using the existing makeShareText() output plus the app URL and opens it (window.location.href = mailto;).
• Wired the new handler with el("emailBtn").addEventListener("click", emailResult); and ensured labels update with language toggles.

Testing

• Launched the app locally with python3 -m http.server 4173 and confirmed the server started successfully.
• Ran an automated Playwright script (mcp__browser_tools__run_playwright_script) that completed a quiz to the result screen and captured a screenshot showing the new Email me button, which succeeded.
• Verified the mailto: URL is constructed from makeShareText() and the app URL by inspecting the flow during the automated run, and observed no runtime errors.

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Codex Task