Git Hooks Module Implementation

Git hooks integration using stackpanel app tooling wrappers. Consumes stackpanel.appsComputed.<app>.wrappedTooling.* and exposes a git-hooks configuration fragment suitable for git-hooks.nix.

Also handles cleanup of stale git hooks that reference garbage-collected nix store paths.

Modules can contribute extra linters/formatters via:

stackpanel.git-hooks.extraLinters = [ <derivation> ... ];
stackpanel.git-hooks.extraFormatters = [ <derivation> ... ];