Follow-up to #369. `resolveInsideRoot` used `filepath.Abs` which does NOT
resolve symlinks — so "workspaces/dev/leaked" where "leaked" is a symlink
to "/etc" would lexically pass the prefix check but resolve outside root.
Fix: call `filepath.EvalSymlinks` before the final prefix check. If the
resolved path points outside root the function returns "path escapes root".
Broken symlinks are also rejected (fail closed).
Also add TestResolveInsideRoot_RejectsSymlinkTraversal covering:
- Symlink pointing outside → rejected (CWE-59)
- Symlink staying inside root → allowed
- Broken symlink → rejected
