docs: clarify query vs prerender on prerendered pages

[RazinShafayet2007]

Closes #15274

This PR clarifies the Remote Functions docs for prerendered pages (export const prerender = true). It adds a note in the query section explaining that query requires a runtime server and can’t be used during prerendering (including when prerender = true is set on a parent +layout), and updates the prerender section note to clarify that prerender functions do work on prerendered pages (including fully static adapter-static builds).

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