refactor: hoist OS-specific package names to role defaults

- nfs_server: nfs_package_name (nfs-utils / nfs-kernel-server)
- wireguard: wireguard_package_name (wireguard-tools / wireguard)
- tooling:   tooling_dig_package, tooling_netcat_package

Also fix tooling role structure: move tooling.yml to tasks/main.yml so
the role is actually invokable via 'role: tooling' (defaults/main.yml
is auto-loaded), and collapse the 10 individual package tasks into a
single list-based install.

roles/nfs_server/defaults/main.yml

@@ -16,3 +16,7 @@ nfs_port: 2049
 
 nfs_server_firewall_allowed_sources:
   - 127.0.0.0/8
+
+# OS-dependent package name
+nfs_package_name: >-
+  {{ (ansible_facts['os_family'] == 'Archlinux') | ternary('nfs-utils', 'nfs-kernel-server') }}