feat(prompts-core): add package skeleton

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

package.json

@@ -11,6 +11,7 @@
     "packages/ast-grep-mcp",
     "packages/utils",
     "packages/model-core",
+    "packages/prompts-core",
     "packages/comment-checker-core",
     "packages/hashline-core",
     "packages/boulder-state",