Clarify what errors are catchable

📚 Subject area/topic

Error handling

📋 Page(s) affected (or suggested, for new content)

• https://docs.astro.build/en/basics/astro-pages/#error
• Maybe the middleware page? We don't show error handling in there but maybe should

📋 Description of content that is out-of-date or incorrect

Follows https://github.com/withastro/astro/issues/12383

prop for any error thrown during rendering

Quoting @Fryuni:

I'd say that sentence is actually the opposite of the technical truth 😅
It happens for every error except those that happen during rendering, since those are on an ongoing stream.
But what is calling the literal renderComponent function and what users might think as rendering might not be the same

🖥️ Reproduction in StackBlitz (if reporting incorrect content or code samples)

No response

Start with the Error section on the Astro Pages documentation page and review the related issue #12383 for the technical context. Check whether the middleware page also needs error-handling guidance. Done means the documentation accurately explains which errors can be caught and avoids implying that errors during an ongoing render stream are handled the same way.