v8 boundary: libnode.dylib distribution in release tarballs

[cs01]

Currently libnode loads from worktree vendor/node/lib/libnode.dylib via rpath. Release tarballs don't bundle it. Users can't use pragma on installed chad.

Ask

• scripts/build-target-sdk.sh includes vendor/node/lib/libnode.* in SDK tarball
• install_name_tool / patchelf rpath rewrite so binary finds libnode alongside
• Decide: always ship libnode (binary +90MB) or lazy-download on first pragma compile

Est

~1 day.
Blocker for curl install users to try pragma.