[12.x] Document static routes - backport

[DGarbs51]

Summary

Backports the Route::static() documentation from the Laravel 13.x docs PR to Laravel 12.x.

The new routing.md section covers:

• basic ->static() usage with shared and browser TTL overrides,
• default config/cache.php options,
• response and middleware behavior,
• when not to use static routes,
• Inertia behavior,
• Livewire compatibility,
• the CDN / Cloudflare Cache Rule caveat.

Backport Notes

The Laravel 13.x docs use Illuminate\Foundation\Http\Middleware\PreventRequestForgery in the default config example. Laravel 12.x uses Illuminate\Foundation\Http\Middleware\ValidateCsrfToken, so this backport adjusts the example accordingly.

Related PRs

• Laravel 12.x framework backport PR: [12.x] Add static route cache support - backport framework#60287
• Laravel 13.x framework PR: [13.x] Add static route cache support framework#60286
• Laravel 13.x docs PR: [13.x] Document static routes #11214

Compatibility Verification

The framework backport PR includes app-level matrix verification across PHP 8.4 / 8.5, Inertia 1 / 2 / 3, and Livewire 3 / 4 for Laravel 12.x where Composer constraints permit those combinations.

Testing

Documentation-only change.