fix: add shrinkwrap lockfile @W-19291869@

[cristiand391]

What does this PR do?

Updates publish-mcp workflow to generate a shrinkwrap lockfile for @salesforce/mcp.

npm shrinkwrap doesn't support monorepos/workspaces:

➜  mcp git:(cd/lockfile) pwd
/Users/cdominguez/code/gh/mcp-shrink/mcp/packages/mcp
➜  mcp git:(cd/lockfile) npm shrinkwrap
npm error code ENOWORKSPACES
npm error This command does not support workspaces.
npm error A complete log of this run can be found in: /Users/cdominguez/.npm/_logs/2025-10-24T20_47_00_712Z-debug-0.log

so when publishing we copy packages/mcp to a single dir and run npm shrinkwrap to generate a lockfile before running npm publishing.

Testing

See lockfile included here:
https://www.npmjs.com/package/@salesforce/mcp/v/0.23.5-dev.1?activeTab=code

install @salesforce/[email protected] and verify tools can be called.

What issues does this PR fix or reference?

@W-19291869@