feat: detect asset version changes during SPA navigation

[adnaan]

After a deployment, users with open tabs have stale CSS/JS. SPA navigation fetches new HTML but uses old client code, which may be incompatible.

Expected behavior: Track asset versions (e.g., via data attribute or response header). If assets changed between navigations, trigger a full page reload instead of SPA navigation.

Reference: Livewire asset tracking, Turbo asset tracking.

Discovered during cross-handler SPA navigation research (PR #58).