#63: Fix HTML5 validation issues

[masteradhoc]

What?

Fixes HTML5 validation issues.

Fixes #63.

Why?

The plugin's output contained several XHTML-isms and non-conforming patterns that fail HTML5 validation

How?

• Remove XHTML-style self-closing void elements — <input />, <img />, <br />, <hr /> → no trailing slash, across all provider and core files.
• Remove XHTML-style boolean attribute — disabled="disabled" → disabled on the profile page fieldset.
• Convert "Copy Codes" from <a> to <button> — the element has no URL destination; <a href="javascript:void(0);"> is non-conforming. The JS targets it by class so no JS changes needed.
• Add href="#" to "Download Codes" <a> — HTML5 requires href when download is present. The JS sets the real data URI href after code generation; # is just a valid placeholder.
• Remove duplicate inline <style> block — the block in class-two-factor-core.php was already moved to user-edit.css by Move class-two-factor-core.php login styles from inline to enqueued stylesheet #807, but was accidentally reintroduced by Move inline JS to external script files #814 while refactoring inline JS. This removes it again.

Note: type="text/javascript" and type="text/css" in includes/ are intentionally left — those files track WordPress Core.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 4.8
Used for: Drafting the implementation and PR text. Code reviewed and edited by me.

Testing Instructions

1. Log in as a user with 2FA enabled — verify the login form renders correctly for TOTP, Email, and Backup Codes providers.
2. Visit your profile page — confirm the Two-Factor Options section displays and saves correctly, including enabling/disabling providers and setting a primary method.
3. On the profile page, generate new backup codes — confirm the Copy and Download buttons work.
4. Run the browser's HTML validator extension against the login page and profile page — no new errors should appear for any of the changed elements.

Screenshots or screencast

Before	After

Changelog Entry

Fixed - Bring plugin HTML output into conformance with the HTML5 spec

[github-actions]

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Co-authored-by: masteradhoc <masteradhoc@git.wordpress.org>
Co-authored-by: kraftbj <kraftbj@git.wordpress.org>

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