[13.x] Document static routes

[DGarbs51]

Summary

Documents the new Route::static() API for Laravel 13.x.

The new section in routing.md 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.

Related PRs

• Laravel 13.x framework PR: [13.x] Add static route cache support framework#60286
• Laravel 12.x framework backport PR: [12.x] Add static route cache support - backport framework#60287
• Laravel 12.x docs backport PR: [12.x] Document static routes - backport #11215

Compatibility Verification

The framework PR includes app-level matrix verification across PHP 8.4 / 8.5, Inertia 2 / 3, and Livewire 3 / 4 for Laravel 13.x. Inertia 1 is not Laravel 13 compatible.

Testing

Documentation-only change.