Simplify PHPStan settings to eliminate environment-specific errors

[priethor]

What

Eliminate environment-specific PHPStan failures between local developmentand CI and improve static analysis configuration.

How

• Configuring reportUnmatchedIgnoredErrors: false so that CI errors we are ignoring are not reported as errors when running locally.
• Cleaning up outdated ignore rules and documentation issues, both in the baseline and in@phpstan-ignore-next-line comments, replacing all with a single ignore pattern.
• Replacing DOING_AJAX constant with wp_doing_ajax() function call
• Add WordPress stubs to PHPStan configuration for better type checking
• Fix PHPDoc parameter formatting to meet coding standards

Testing Instructions

1. Run composer test:phpstan to verify no PHPStan errors