feat(system-config): add system service configuration role

Port global-systemServiceConfigurationFiles() and
global-postPackageConfiguration().

Manages:
- Global zsh config (/etc/zshrc)
- Mail aliases and postfix relay (local-only, smarthost to Cloudron)
- Static DNS resolv.conf (replaces systemd-resolved symlinks)
- rsyslog forwarding to LibreNMS (skipped on LibreNMS server itself)
- DHCP client config (skipped on DHCP servers pfv-netinfra-01/02)
- SNMP daemon config selected by host class (Pi/physical/Proxmox/VM)
- NTP client config (skipped on NTP server hosts)
- LLDP network discovery
- Cockpit disallowed-users
- Default user shells (zsh, conditional on user existence)
- Process accounting (accton)
- CPU governor on physical/Proxmox hosts (performance)
- tuned profile on VM guests (virtual-guest)

Infrastructure configs use Jinja2 templates parameterized by variables
in group_vars/all.yml.

🤖 Generated with [Crush](https://github.com/charmassociates/crush)

Assisted-by: GLM-5 via Crush <crush@charm.land>

roles/system_config/handlers/main.yml

@@ -0,0 +1,43 @@
+---
+- name: Update aliases db
+  ansible.builtin.command: newaliases
+  changed_when: true
+
+- name: Restart rsyslog
+  ansible.builtin.systemd:
+    name: rsyslog
+    state: restarted
+
+- name: Postmap generic
+  ansible.builtin.command: postmap /etc/postfix/generic
+  changed_when: true
+
+- name: Restart postfix
+  ansible.builtin.systemd:
+    name: postfix
+    state: restarted
+
+- name: Restart snmpd
+  ansible.builtin.systemd:
+    name: snmpd
+    state: restarted
+    daemon_reload: true
+
+- name: Restart lldpd
+  ansible.builtin.systemd:
+    name: lldpd
+    state: restarted
+
+- name: Restart cockpit
+  ansible.builtin.systemd:
+    name: cockpit
+    state: restarted
+
+- name: Restart ntpsec
+  ansible.builtin.systemd:
+    name: ntpsec.service
+    state: restarted
+
+- name: Daemon reload
+  ansible.builtin.systemd:
+    daemon_reload: true