build(deps): upgrade docs toolchain to vite 8 (rolldown) to drop vulnerable esbuild

vite 8 replaces esbuild with rolldown and demotes esbuild to an optional
peer at the patched ^0.27||^0.28 range, so the transitive esbuild 0.25
(GHSA-gv7w-rqvm-qjhr, dev-only via vitepress) leaves the resolved tree.
vitepress 1.6.4 builds on vite 8 via compat shims; full suite + docs
build + bun audit all green.

(cherry picked from commit da0366c779e3cc3009ca9445fdfe4184770db79b)