Export: Stabilize pattern sanitization

[MaggieCabrera]

Summary

Repeat pattern sanitization until the exported content is stable.

This keeps adjacent fragments from forming a new removable sequence after an earlier replacement.

Test plan

• vendor/bin/phpunit -c phpunit.xml.dist --verbose --filter Test_Create_Block_Theme_Patterns
• vendor/bin/phpcs --standard=phpcs.xml.dist includes/create-theme/theme-patterns.php tests/test-theme-patterns.php
• Confirmed overlapping and legacy-script variants remain parse-clean while ordinary block markup is preserved.

[Copilot]

Pull request overview

This PR improves the export pipeline’s defense-in-depth for wp_block pattern bodies by ensuring PHP-tag sanitization is applied repeatedly until the content no longer changes, preventing adjacent fragments from combining into newly-detectable PHP open-tag sequences after earlier removals.

Changes:

• Update CBT_Theme_Patterns::strip_php_tags() to iterate sanitization passes until the output is stable.
• Add PHPUnit coverage for overlapping <? fragments and for cases where legacy <script language="php">…</script> removal can expose new <? sequences.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
includes/create-theme/theme-patterns.php	Makes strip_php_tags() repeat sanitization passes until no further changes occur, preventing bypass via adjacent-fragment recombination.
tests/test-theme-patterns.php	Adds tests that assert sanitization stability for overlapping-open-tag and legacy-script-removal edge cases.

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