[6.x] Do not set the Inertia root view globally

[lazerg]

CpServiceProvider::boot() set the Inertia root view globally with Inertia::setRootView('statamic::layout'), so apps that render their own Inertia frontend outside the control panel inherited it and their pages (including Inertia error responses) rendered inside Statamic's CP layout. The control panel already sets its own root view via the HandleInertiaRequests middleware on every CP route, so the global call isn't needed and just leaks into the host app.

Fixes#14619

[lazerg]

@jasonvarga mind reviewing this when you have a moment, it removes a redundant global Inertia root-view call that was leaking into host apps outside the CP.

[duncanmcclean]

Thanks for the PR. We'll review it when we can.

In the meantime, you can pull this PR into your project with a composer patch.

[jasonvarga]

Thanks for this — moving the rootView to HandleInertiaRequests is the right call.

One edge case: exception rendering for CP routes can happen before HandleInertiaRequests has run, so the root view wasn't always set yet — it fell back to Inertia's default (app) and crashed with View [app] not found.

Pushed a follow-up commit that pins ->rootView(...) explicitly in RendersControlPanelExceptions and RendersHttpExceptions, backed by a new HandleInertiaRequests::ROOT_VIEW constant. The RendersHttpExceptions one wasn't technically hitting the bug, but added it there too for consistency.