fix: declare zod runtime dependencies

[mturac]

Summary

• add zod as a direct runtime dependency for the memory and sequential-thinking servers
• add the same direct dependency for the filesystem server, which also imports zod directly
• update the npm lockfile so published package installs include the dependency metadata

Fixes #4330

Testing

• npm install
• npm run build --workspace src/memory && npm run build --workspace src/sequentialthinking && npm run build --workspace src/filesystem
• npm test --workspace src/memory && npm test --workspace src/sequentialthinking && npm test --workspace src/filesystem
• packed the three affected workspaces and installed the tarballs in a clean temp project
• verified zod resolves from each installed package and that short startup smokes no longer hit a missing zod module error
• git diff --check