feat(compat): Add Laravel 13 support

[mikebronner]

Summary

Add Laravel 13 compatibility to the package by updating composer.json version constraints, CI matrix, and documentation.

Acceptance Criteria

• composer.json version constraint updated to include Laravel 13.x (e.g. ^10.0|^11.0|^12.0|^13.0)
• CI matrix includes a Laravel 13 job and all tests pass with zero failures on Laravel 13
• Any Laravel 13 breaking changes affecting this package are identified and resolved
• README version support table updated to include Laravel 13
• composer update completes without conflicts under Laravel 13

Fixes #56

[mikebronner]

Review Checklist

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

• phpunit.xml.dist references non-existent tests/Feature directory: Running vendor/bin/phpunit fails immediately with "Test directory not found." The CI workflow runs vendor/bin/phpunit without any flags, so this will also fail in CI. Either remove the Feature testsuite from phpunit.xml.dist or create the directory.
• phpunit.xml.dist uses deprecated PHPUnit 9 attributes: backupStaticAttributes, convertErrorsToExceptions, convertNoticesToExceptions, convertWarningsToExceptions, and the old <coverage> format are all removed/changed in PHPUnit 10+/11. This config needs to be modernized.
• No non-browser tests exist: The only test requires Chromedriver/Dusk. AC requires tests passing — zero runnable tests doesn't meet that bar. Add at least a basic integration test (service provider boots, routes registered, etc.).
• PHP constraint bumped from ^8.1 to ^8.2 without explanation: The PR title is about Laravel 13 support, but the PHP floor was raised from 8.1 to 8.2. This is fine if intentional (Laravel 13 requires 8.3+), but note that the CI matrix also runs PHP 8.2 + Laravel 13 which should be excluded since Laravel 13 requires PHP 8.3+. The exclude block only removes php: 8.2 / laravel: 13.* — good, that's correct. But confirm the PHP floor bump is intended.
• CI uses wildcard version syntax (10.*) vs caret (^10.0): Inconsistent with composer.json which uses ^10.0. While functionally similar for the composer require command, it's better to be consistent. Minor nit — not a blocker.

[mikebronner]

Review Complete ✅

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

composer.json updated with ^13.0 for illuminate/support, testbench, testbench-browser-kit, and testbench-dusk. CI matrix properly covers PHP 8.2–8.4 × Laravel 10–13 with correct exclusion (PHP 8.2 + Laravel 13). phpunit.xml.dist modernized. New ServiceProviderTest with thorough config key assertions. README version table is clear.

PHP minimum bumped from ^8.1 to ^8.2 — correct for the supported Laravel range.

Ready for your final review and merge.