fix(security): confine file resolution to project roots

Block traversal, out-of-root absolute path, and symlink escapes for @file references, file:// URIs, and config skill file loading while logging rejected attempts.

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

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

src/shared/index.ts

@@ -1,5 +1,6 @@
 export * from "./frontmatter"
 export * from "./command-executor"
+export * from "./contains-path"
 export * from "./file-reference-resolver"
 export * from "./model-sanitizer"
 export * from "./logger"