[F] Add preview route + submit links

[1aurend]

Utilizes draft mode to skip cached entity data and avoid caching admin-only data without duplicating the page tree under a /preview route segment. This PR also updates how auth state is tracked to ensure that both client and server relay environments are in sync and aren't reliant on render-based checks via hooks.

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Project	Deployment	Actions	Updated (UTC)
meru-client	Ready	Preview, Comment	Jun 2, 2026 12:46am

[1aurend]

@dananjohnson I know you're not super familiar with this project, but would you mind 👀 this to see if anything I'm doing here jumps out at you as a problem? I couldn't use the standard next-auth hooks to sync session across client and server for a couple of reasons:

1. The two relay environments— waiting a render for the useSession hook to find the token and supply it to the client relay env for client-side refetches was causing relay to error with null fragments.
2. Because we're caching, but also allowing to users to effectively "view drafts" at the same URL and not in a container like an iframe in the CMS, we needed a way to ensure that both viewer data and entity data that requires auth is never cached.