chore: set msgpackr-extract build approval to false
The placeholder 'set this to true or false' was an invalid value that tripped
pnpm's build-script approval gate (ERR_PNPM_IGNORED_BUILDS) on install/test.
msgpackr-extract is an optional native build we don't need; pin it false.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>