[6.x] Lazy load Inertia page components

[jasonvarga]

Summary

Switches the Inertia page resolver from eager to lazy import.meta.glob, so each CP page is split into its own chunk and fetched on demand.

The previous version eagerly imported every .vue file under resources/js/pages/ into the main bundle. Now import.meta.glob returns a map of dynamic imports, and the resolver awaits the matching one.

This is one part extracted from #14512

Impact

The initial index-*.js bundle drops from ~230 KB to ~94 KB on a fresh load. Per-page navigation cost is unchanged in practice — the chunk fetch overlaps with Inertia's existing data request.

Test plan

• Production build splits pages into per-page chunks
• Navigation between pages works on Slow 3G with no broken UI (only the expected loading bar)
• Offline navigation behavior matches the previous branch (request fails, no regression)
• Addon page resolution (inertia.get(name)) still works
• NonInertiaPage Blade fallback still renders