[codex] Use scoped cspec package import

[lzrscg]

Summary

• Update editor demo data and README examples to import runtime helpers from @modularcloud/cspec.
• Change the parser to recognize only the scoped runtime package import.
• Add a focused parser test that rejects the old bare "cspec" runtime import as a recognized cspec import.

Root Cause

The examples and parser still used the project shorthand / CLI command name cspec, even though the published package users install and import is @modularcloud/cspec.

Validation

• npm test -w @modularcloud/cspec-core
• npm test