Document catchError for the Pages Router (#97748)
Supersedes https://github.com/vercel/next.js/pull/91848
`catchError` works in both the App Router and Pages Router, but its API
reference only documented the App Router behavior. This adds a Pages
Router reference backed by the same canonical document and scopes the
content that differs between routers.
The Pages Router examples use `reset()` because `retry()` is App
Router-only, omit App Router-only navigation behavior, and use Pages
Router component paths. The existing App Router guidance and shared API
reference remain unchanged.
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