## Problem
When logging in with a `?redirect=`, the target page may crash. This
happens because the update from `SyncClientConfig` is applied in a
`useEffect`, which runs **_after_** the target page's client components
render. As a result, those components read the unauthenticated client
config on first render - even though they expect the authenticated one.
## Steps To Reproduce
1. logout
2. login with ?redirect=
3. document client component incorrectly still receives unauthenticated
client config on render
4. THEN the SyncClientConfig useEffect runs. Too late
5. Potential error (depending on the page, e.g. document view) -
document client component expects sth to be there, but it is not
## Solution
This PR replaces `SyncClientConfig` with a `RootPageConfigProvider`.
This new provider shadows the root layout’s `ConfigProvider` and ensures
the correct client config is available **_immediately_**.
It still updates the config using `useEffect` (the same
way`SyncClientConfig` did), but with one key difference:
- During the brief window between the redirect and the effect running,
it overrides the root layout’s config and provides the fresh,
authenticated config from the root page via the `RootConfigContext`.
This guarantees that client components on the target page receive the
correct config on first render, preventing errors caused by reading the
outdated unauthenticated config.
## Additional change - get rid of `UnsanitizedClientConfig` and
`sanitizeClientConfig`
Those functions added unnecessary complexity, just to build the
blocksMap. I removed those and perform the building of the `blocksMap`
server-side - directly in `createClientConfig`.
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13af91f05d