fix(prompts-core): block prompt path traversal

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

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

packages/prompts-core/src/index.ts

@@ -8,4 +8,4 @@ export type {
 } from "./types"
 export { resolveVariant } from "./variant-resolver"
 export type { ResolveVariantInput } from "./variant-resolver"
-export { loadPrompt, PromptFileNotFoundError } from "./loader"
+export { loadPrompt, PromptFileNotFoundError, PromptPathTraversalError } from "./loader"