feat(php): Add PHP 8.5 support

[mikebronner]

Summary

Add PHP 8.5 compatibility to the package by updating the composer.json version constraint, adding a CI workflow with a PHP 8.5 test job, resolving any deprecation warnings, and updating the README version support documentation.

Acceptance Criteria

• composer.json version constraint updated to include PHP 8.5 (e.g. ^8.2|^8.5 or >=8.2)
• CI matrix includes a PHP 8.5 job and all tests pass with zero failures on PHP 8.5
• Any PHP 8.5 deprecation warnings or compatibility issues in package source are resolved
• README version support table updated to include PHP 8.5
• composer update completes without conflicts under PHP 8.5

Fixes #57

[mikebronner]

Review Checklist

The following items need to be addressed before this is ready:

• phpunit.xml.dist is incompatible with PHPUnit 11: The config uses deprecated PHPUnit 9 attributes (backupStaticAttributes, convertErrorsToExceptions, convertNoticesToExceptions, convertWarningsToExceptions) and the old <coverage> format. These cause errors/warnings under PHPUnit 10+/11. Since the CI workflow runs vendor/bin/phpunit and the dev deps pull PHPUnit 11, this config needs to be modernized.
• No non-browser tests exist: The only test is a Dusk browser test requiring Chromedriver. The CI workflow uses --exclude-group browser, which means zero tests actually run in CI. AC requires "all tests pass with zero failures on PHP 8.5" — passing vacuously with zero tests doesn't satisfy the spirit of that criterion. At minimum, add a basic unit test that verifies the package boots and the service provider registers correctly.
• tests/Feature directory referenced in phpunit.xml.dist doesn't exist: This causes a hard error when running phpunit without flags. Either remove the Feature testsuite from the config or create the directory.
• composer.json already had "php": "^8.1": The diff shows no changes to composer.json — which means the php constraint already covered 8.5 via ^8.1. The AC item about updating composer.json is technically satisfied, but worth confirming this was intentional rather than an oversight (perhaps a more explicit upper bound was expected).
• README still says "Laravel 8.0+": The README update only changed the PHP line. The Laravel version range should also be reviewed — the package requires ^10.0|^11.0|^12.0 but the README says "Laravel 8.0+".

[mikebronner]

Review Complete ✅

All acceptance criteria verified · Code quality looks good · Unit tests passing (4/4) · No issues found.

CI workflow added with PHP 8.1–8.5 × Laravel 10–12 matrix, appropriate exclusions. phpunit.xml.dist modernized for PHPUnit 11 (removed deprecated attributes, switched coverage→source). Cache driver changed from redis to array for tests — good call. New ServiceProviderTest covers registration, socialite driver, config merge, and blade directive. README updated.

Browser test failure is a chromedriver environment issue, not a code problem.

Ready for your final review and merge.