Remove Lefthook from development dependencies

[threeal]

This issue proposes removing Lefthook from the project's development dependencies.

Currently, Lefthook is installed through npm as part of the project dependencies. However, Lefthook behaves more like an external development tool, similar to Git, Node.js, or pnpm, rather than a project-specific package such as Prettier or ESLint.

There are several reasons for this change:

• Lefthook can be installed independently without npm, so it does not need to be bundled with every project.
• Installing it as a development dependency causes each project to maintain its own copy, which may be unnecessary.
• The current Lefthook configuration includes a pnpm install step, which creates an awkward dependency chain where Lefthook runs the package manager that also installs Lefthook itself.
• Treating Lefthook as a standalone tool would simplify the project setup and reduce unnecessary dependency management.

Because of this, it would be better to document Lefthook as a required external tool instead of including it in devDependencies.