Fixed - Filter Guidelines service queries by wp_guideline_type=content

[itsgajendraSingh]

Summary

• Adds a GUIDELINE_TYPE_TAXONOMY constant (wp_guideline_type) and a private GUIDELINE_TYPE_CONTENT constant (content) to the Guidelines service.
• When the wp_guideline_type taxonomy is registered (Gutenberg 23.1+), fetch_guidelines() now appends a tax_query to restrict the query to posts assigned the content term, preventing a newer artifact guideline from shadowing the intended content guideline during prompt assembly.
• Falls back to the previous unfiltered query on sites running Gutenberg < 23.1 where the taxonomy does not exist.

Fixes #529.

Changes

• includes/Services/Guidelines.php — add constants, conditionally add tax_query in fetch_guidelines().
• tests/Integration/Includes/Services/Guidelines_CPT_Helpers.php — add register_guideline_type_taxonomy() helper; extend create_guidelines_post() with an optional $guideline_type parameter.
• tests/Integration/Includes/Services/Guidelines_Test.php — add two new tests covering the mixed artifact/content scenario and the untyped-post edge case.

Test plan

• Existing Guidelines_Test suite still passes.
• test_get_guidelines_ignores_artifact_type_when_taxonomy_exists confirms the content guideline is returned when a newer artifact guideline also exists.
• test_get_guidelines_returns_null_for_untyped_post_when_taxonomy_exists confirms untyped posts are excluded when the taxonomy is present.
• Manual: install Gutenberg 23.1.x, reproduce steps from Filter Guidelines service queries by content guideline type #529, verify the correct content guideline is used in prompt assembly.

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