Add PHPUnit test suite and GitHub Actions CI

[joehoyle]

Summary

• Adds PHPUnit test infrastructure using the WordPress test framework (wp-phpunit) with integration tests against a real MySQL database
• 61 tests covering Model, Query, QueryResults, Table, namespace helpers, Relations, Term, Importer, and REST Controller
• GitHub Actions CI running across PHP 7.4, 8.0, 8.1, 8.2 with MySQL 8.0

Test coverage

Class	Tests	What's covered
QueryTest	4	WHERE clauses, comparison operators, OR relation, pagination
ModelTest	8	CRUD, state flags, query integration, pagination, reload
QueryResultsTest	5	Count, iteration, array access, total available, as_array
TableTest	8	ensure_table create/conform, parse_index variants
NamespaceFunctionsTest	4	get_primary_column, save_many atomic/rollback/dry_run
RelationsTest	10	Relationship table creation, HasManyAssociation add/remove/get, parent scoping, RelationalQuery, relationship filtering
TermTest	8	from_term, from_id, as_term roundtrip, save/delete return errors, table name/schema
ImporterTest	4	Batch insert, update existing, dry run, result counts
ControllerTest	9 (1 skipped)	Route registration, CRUD via REST, 404 handling, ID rejection, self links

Notes

• ControllerTest::test_get_items is skipped: Controller::get_items passes WP default pagination params (page/per_page) as WHERE clauses to Query, causing an undefined array key error. This is an upstream bug.
• TermTest::test_from_id_throws_for_invalid documents that Term::from_id() does not handle get_term() returning null (passes it to from_term() which throws TypeError).

Files

• composer.json — dev deps: phpunit, wp-phpunit, roots/wordpress-no-content, phpunit-polyfills
• phpunit.xml.dist — PHPUnit 9 config
• tests/bootstrap.php + tests/wp-tests-config.php — WP test framework bootstrap
• tests/helpers/ — Test_Model, Failing_Test_Model, Test_Parent_Model, Test_Child_Model, Test_Importer, Test_Controller
• tests/database/ — Query, Model, QueryResults, Table, NamespaceFunctions, Relations tests
• tests/builtin/ — Term tests
• tests/api/ — Controller tests
• tests/ImporterTest.php — Importer tests
• .github/workflows/phpunit.yml — CI matrix (PHP 7.4-8.2, MySQL 8.0)
• .gitignore — excludes vendor/, composer.lock, phpunit cache

Running locally

composer install
mysql -u root -e "CREATE DATABASE IF NOT EXISTS foundry_tests"
vendor/bin/phpunit

Test plan

• All 61 tests pass locally (60 pass, 1 skipped with documented reason)
• CI passes across PHP 7.4-8.2