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### What?
Improve the `errors/large-page-data.mdx` error page.

### Why?
The existing error page lacked clarity on the `__NEXT_DATA__` mechanism,
performance impacts, configuration options, and its applicability solely
to the Pages Router. This led to confusion, as highlighted in community
discussions:
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#38364 (comment)
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#60193 (comment)

### How?
- Added a note clarifying this warning applies only to the Pages Router.
- Explained the `__NEXT_DATA__` mechanism, why the threshold exists, and
its performance implications (page weight, hydration, memory).
- Provided actionable suggestions to reduce data size (filter, paginate,
client-side fetching).
- Documented the `experimental.largePageDataBytes` configuration option
with a `next.config.js` example.
- Included relevant external links for further reading.

Closes NEXT-
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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Joseph <icyJoseph@users.noreply.github.com>