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

tests/test_server.py

@@ -43,25 +43,6 @@ class TestWsUrlGeneration:
         assert b"ws://[::1]:9090/ws" in resp.data
 
 
-class TestApiStatusAll:
-    @patch("webui.server.get")
-    def test_success(self, mock_get, client):
-        mock_get.return_value = {"firewall": {"zones": {}}, "dnsmasq": {}}
-        resp = client.get("/api/status/all")
-        assert resp.status_code == 200
-        data = resp.get_json()
-        assert data["ok"] is True
-        assert "firewall" in data["data"]
-
-    @patch("webui.server.get")
-    def test_error(self, mock_get, client):
-        mock_get.side_effect = RuntimeError("connection refused")
-        resp = client.get("/api/status/all")
-        assert resp.status_code == 500
-        data = resp.get_json()
-        assert data["ok"] is False
-
-
 class TestBlueprintsRegistered:
     def test_all_blueprints_registered(self, client):
         from webui.server import BLUEPRINTS