feat: Add marko/inertia-react package

[ps-carvalho]

Summary

PR 3/5 in the Vite + Inertia package-import sequence. This revises marko/inertia and marko/inertia-react per maintainer feedback:

• Adds parent-owned inertia.assetEntry and inertia.ssr.bundle slots to marko/inertia.
• Defaults Inertia::render() to config('inertia.assetEntry') when no asset entry is passed.
• Adds Marko\Inertia\Frontend\InertiaFrontendInterface as a frontend marker contract.
• Changes marko/inertia-react to overlay config/inertia.php, dropping the unused config/inertia-react.php and PHP ssrEntry key.
• Adds a React marker binding through module.php so multi-install conflicts are loud through the existing binding registry mechanism.
• Updates docs to omit the per-render asset string and use unpinned npm install commands.

Maintainer Feedback Addressed

• No pseudo-functionality: the shipped config now overlays keys consumed by marko/inertia.
• Multi-install protection: the companion registers the frontend marker binding instead of relying on silent config merge order.
• Build-time/runtime split: ssrEntry is no longer shipped in PHP config.
• Version guidance: npm commands are unpinned and point to Inertia.js for current adapter support.
• Package-count tests remain derived; no count bump included.

Test Plan

• vendor/bin/pest packages/inertia/tests packages/inertia-react/tests --colors=never
• vendor/bin/phpcs --standard=phpcs.xml packages/inertia packages/inertia-react
• vendor/bin/php-cs-fixer fix packages/inertia --dry-run --diff --using-cache=no
• vendor/bin/php-cs-fixer fix packages/inertia-react --dry-run --diff --using-cache=no
• composer validate --strict --no-check-lock packages/inertia-react/composer.json
• composer validate --strict --no-check-lock
• vendor/bin/pest tests/IntegrationVerificationTest.php tests/PackagingTest.php packages/inertia/tests packages/inertia-react/tests --colors=never