Refactor systemctl service handling with @ support

- Unified variable naming: system_service_id → systemctl_id
- Added automatic removal of trailing '@' for role directory resolution
- Improved first_found search: prefer target role, fallback to sys-systemctl defaults
- Split template resolution logic to avoid undefined variable errors
- Added assertion in sys-timer to forbid '@' in systemctl_id
- Corrected default systemctl.service.j2 template description
- Cleaned up path handling and script directory generation

Context: conversation about fixing template resolution and @ handling
https://chatgpt.com/share/68a39994-1bb0-800f-a219-109e643c3efb

filter_plugins/get_service_script_path.py

@@ -1,18 +1,18 @@
 # filter_plugins/get_service_script_path.py
 # Custom Ansible filter to generate service script paths.
 
-def get_service_script_path(system_service_id, script_type):
+def get_service_script_path(systemctl_id, script_type):
     """
-    Build the path to a service script based on system_service_id and type.
+    Build the path to a service script based on systemctl_id and type.
 
-    :param system_service_id: The identifier of the system service.
+    :param systemctl_id: The identifier of the system service.
     :param script_type: The script type/extension (e.g., sh, py, yml).
     :return: The full path string.
     """
-    if not system_service_id or not script_type:
-        raise ValueError("Both system_service_id and script_type are required")
+    if not systemctl_id or not script_type:
+        raise ValueError("Both systemctl_id and script_type are required")
 
-    return f"/opt/scripts/{system_service_id}/script.{script_type}"
+    return f"/opt/scripts/{systemctl_id}/script.{script_type}"
 
 
 class FilterModule(object):