#8834: Use filtered admin URLs in do_robots()

[masteradhoc]

Updates do_robots() to use filtered admin URL paths instead of hardcoded /wp-admin/ values.

This changes the default robots.txt output to derive the Disallow and Allow paths from admin_url() and admin_url( 'admin-ajax.php' ), while continuing to output only the path portion. This allows installs that filter admin URLs to generate correct robots.txt directives.

A PHPUnit regression test is included to verify that filtered admin paths are reflected in the do_robots() output.

Trac ticket: https://core.trac.wordpress.org/ticket/63467

Use of AI Tools

AI assistance: Yes
Tool(s): GitHub Copilot
Model(s): GPT-5.4
Used for: Drafting the initial patch and regression test. The final implementation, test coverage, and PR description were reviewed and edited by me.

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