Abilities API: Make the ability category optional

[gziolo]

This makes the category argument optional when registering an ability. When it is omitted, the registry assigns the built-in uncategorized category.

Previously, the registry only validated a category when one was provided, but WP_Ability still required the argument during instantiation. This left registrations without a category unable to succeed. Applying the fallback before validation keeps explicit invalid category values rejected while allowing simple or transitional registrations to omit a category.

The change:

• registers the uncategorized category with the other core ability categories;
• defaults an omitted category to uncategorized;
• relies on the category lookup's string type declaration to reject invalid types;
• requires provided category strings, including an empty string, to name a registered category;
• updates the public API documentation; and
• adds regression coverage for the fallback and invalid category values.

Props @Sachin7907 for the patch and @itzmekhokan for feedback.

Trac ticket: https://core.trac.wordpress.org/ticket/65569

Testing

• git diff --check passes.
• PHPCS passes for all changed PHP files.
• wpAbilitiesRegistry.php: 37 tests, 71 assertions.
• wpRegisterAbility.php: 20 tests, 50 assertions.
• wpRegisterCoreAbilities.php: 14 tests, 131 assertions.

Use of AI Tools

AI assistance: Yes
Tool(s): OpenAI Codex
Model(s): GPT-5
Used for: Reviewing the existing local diff, running validation, and preparing the commits and pull request description. The implementation was reviewed by the submitter.

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[github-actions]

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Props gziolo.

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[Copilot]

Pull request overview

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