feat: add system metrics dashboard with resource monitoring

- Add system metrics endpoint (CPU load, memory, swap, network traffic)
- Collect metrics from /proc and /sys (no subprocess required)
- Overhaul dashboard to pull from per-subsystem models
- Remove deprecated /status/all monolithic endpoint
- Improve networkd import to handle optional priority prefix
- Fix CSS duplicate .grid-4 rule and unused dashboard imports

daemon/handlers/system.py

@@ -0,0 +1,35 @@
+"""System metrics handler.
+
+Returns CPU load, memory usage, and per-interface network traffic stats.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+from daemon.iface import GET_SYSTEM_METRICS
+from daemon.server import registry
+from lib.state import state as state_store
+
+logger = logging.getLogger(__name__)
+
+
+@registry.register(GET_SYSTEM_METRICS)
+def system_metrics(_request: Any, _body: Any) -> dict[str, Any]:
+    """Return system-wide metrics.
+
+    Reads from pre-collected state (CPU load, memory, network traffic).
+
+    Returns:
+        Dict with load, memory, swap, and traffic data.
+    """
+    sys_state = state_store.get("system")
+    if sys_state is None:
+        return {
+            "load": {"load1": 0.0, "load5": 0.0, "load15": 0.0},
+            "memory": {"total": 0, "available": 0, "used": 0, "used_pct": 0},
+            "swap": {"total": 0, "used": 0, "used_pct": 0},
+            "traffic": {},
+        }
+    return sys_state