dev: scaffold WordPress plugin wrapper

[justlevine]

What

This PR adds the required scaffolding to use MCP Adapter as a WordPress Plugin

Important

This PR is based on #16 which should be merged first.
Relevant diff: d5b9157

What's Included

• Create plugin entrypoint files.
• Remove Jetpack Autoloader dependency (in favor of Composer's built-in)
• Add wp-env.json and use it for linting/ PHPUnit testing
• Add a release.yml to add the built plugin as a GitHub Release artifact
• Update README.md and CONTRIBUTING.md with new commands

Not Included

• An internal review of src (a wholly separate task)
• Rename src to includes (follow-up PR)
• Fix failing tests/remediations (follow-up PR)

To Test

Follow the updated CONTRIBUTING.md#installation steps:

## If you're using NVM, make sure to use the correct Node.js version:
nvm use

## Then install the NPM dependencies:
npm install

## If you are using Composer locally, also run:
composer install

## Start the test environment
npm run wp-env start

## Run the tests
npm run test:php

(Assumedly the failing tests are because the API is not compatible with Abilities API. #13 will lint for that)

[justlevine]

Note: Copilot is useless here because it's picking up both #16 and #14

[galatanovidiu]

It is too big to go through each line of code, but even if there are issues, we can address them later

[Copilot]

Pull Request Overview

This PR transforms the MCP Adapter from a standalone library into a canonical WordPress plugin, adding essential plugin infrastructure and updating the development workflow to use wp-env.

• Scaffolds WordPress plugin wrapper with main plugin file and autoloader
• Removes Jetpack Autoloader dependency in favor of standard Composer autoloading
• Updates development environment to use wp-env for local testing and linting

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
mcp-adapter.php	Main plugin entry point with constants and initialization
src/Plugin.php	Plugin wrapper class implementing singleton pattern
src/Autoloader.php	Custom PSR-4 autoloader with fallback and admin notices
tests/bootstrap.php	Simplified test bootstrap for wp-env integration
.wp-env.json	WordPress development environment configuration
composer.json	Updated dependencies removing Jetpack Autoloader
package.json	Added wp-env scripts and build commands
.github/workflows/release.yml	GitHub Actions workflow for plugin release automation
phpcs.xml.dist	Added main plugin file to PHPCS scanning
README.md	Updated installation and usage documentation
CONTRIBUTING.md	Added wp-env development workflow instructions

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[justlevine]

Synced with trunk, to have the CI - including PHPUnit (also made the diff smaller).

Follow up PRs:

• Rename src => to includes
• Audit/review and remediate lints (including syncing w. latest WP_Ability)
• Deduplicating/updating readme and docs