Use site host in backup codes download title

[faithcoder]

What?

Use the site's host instead of its full URL in the heading of downloaded backup-code files, and make the heading filterable.

Fixes #957

Why?

The current heading includes the scheme and path from home_url( '/' ), which makes the recovery-code file contain a directly usable target URL. The host alone still identifies the site while matching the existing translator comment and avoiding unnecessary URL details.

How?

• Parse the host from home_url() with wp_parse_url().
• Add the two_factor_backup_codes_download_title filter, including the generated title and user as arguments.
• Add REST API regression coverage confirming that the download contains the host but not the full home URL and that the title can be filtered.

Use of AI Tools

AI assistance: Yes
Tool(s): Codex
Model(s): GPT-5
Used for: Investigating the issue, implementing the change, adding tests, and running validation. The resulting diff was reviewed before submission.

Testing Instructions

1. Generate backup codes for a user through the REST API or user profile.
2. Download the recovery-code file.
3. Confirm its heading contains only the site's host, without the URL scheme or path.
4. Add a callback to two_factor_backup_codes_download_title, generate codes again, and confirm the custom heading appears.

Validation performed:

• PHP syntax checks passed for both changed files.
• PHPCS passed for both changed files.
• PHPStan passed for the changed provider.
• git diff --check passed.
• The full PHPUnit suite was not run because the required Docker environment was unavailable.

Changelog Entry

Fixed - Use the site host instead of the full URL in backup-code download headings and allow the heading to be filtered.

[github-actions]

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Co-authored-by: faithcoder <faithcoder@git.wordpress.org>
Co-authored-by: dknauss <dpknauss@git.wordpress.org>

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