chore(cutover): delete the .objectstack-pin snapshot manifests from the merged tree (objectstack#25803)

Bill item 21(b): the seven .objectstack-pin/*/package.json files are the objectui pin build's
link targets. In the merged tree @objectstack/* resolve as workspace:^ members, nothing
installs from file:.objectstack-pin, and the pin script retires with 4a / PR B. The scripts and
tests that name the directory build it in a scratch dir; none reads the committed manifests.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CUXv64KLMfYv3ia2sWi6te

Author: claude