fix: scope mandatory deny paths to the sandbox workdir

[jy-tan]

Summary

Root mandatory dangerous-path protection in the command's actual working directory instead of ambient process cwd, so macOS deny rules stay workspace-scoped without missing protected files in temp workspaces or overmatching paths outside the repo.

Resolves #117.

Changes

• Replace unscoped macOS **/... mandatory deny globs with workspace-rooted recursive patterns while keeping explicit home-directory protection for shell and git dotfiles
• Add workdir-aware sandbox wrapping so macOS and Linux derive mandatory deny roots from the command's execution directory, not the wrapper process cwd
• Update integration and regression coverage to verify scoped deny patterns, generated macOS write rules, and protected .git/hooks, .git/config, and shell config files in temp workspaces

[cubic-dev-ai]

No issues found across 3 files