feat: add System Health monitoring mode

Real-time dashboard for host metrics (CPU, memory, disk, temperatures),
active decoder process status, and SDR device enumeration via SSE streaming.
Auto-connects when entering the mode with graceful psutil fallback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_system.py

@@ -0,0 +1,89 @@
+"""Tests for the System Health monitoring blueprint."""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock, patch
+
+
+def _login(client):
+    """Mark the Flask test session as authenticated."""
+    with client.session_transaction() as sess:
+        sess['logged_in'] = True
+        sess['username'] = 'test'
+        sess['role'] = 'admin'
+
+
+def test_metrics_returns_expected_keys(client):
+    """GET /system/metrics returns top-level metric keys."""
+    _login(client)
+    resp = client.get('/system/metrics')
+    assert resp.status_code == 200
+    data = resp.get_json()
+    assert 'system' in data
+    assert 'processes' in data
+    assert 'cpu' in data
+    assert 'memory' in data
+    assert 'disk' in data
+    assert data['system']['hostname']
+    assert 'version' in data['system']
+    assert 'uptime_seconds' in data['system']
+    assert 'uptime_human' in data['system']
+
+
+def test_metrics_without_psutil(client):
+    """Metrics degrade gracefully when psutil is unavailable."""
+    _login(client)
+    import routes.system as mod
+
+    orig = mod._HAS_PSUTIL
+    mod._HAS_PSUTIL = False
+    try:
+        resp = client.get('/system/metrics')
+        assert resp.status_code == 200
+        data = resp.get_json()
+        # These fields should be None without psutil
+        assert data['cpu'] is None
+        assert data['memory'] is None
+        assert data['disk'] is None
+    finally:
+        mod._HAS_PSUTIL = orig
+
+
+def test_sdr_devices_returns_list(client):
+    """GET /system/sdr_devices returns a devices list."""
+    _login(client)
+    mock_device = MagicMock()
+    mock_device.sdr_type = MagicMock()
+    mock_device.sdr_type.value = 'rtlsdr'
+    mock_device.index = 0
+    mock_device.name = 'Generic RTL2832U'
+    mock_device.serial = '00000001'
+    mock_device.driver = 'rtlsdr'
+
+    with patch('utils.sdr.detection.detect_all_devices', return_value=[mock_device]):
+        resp = client.get('/system/sdr_devices')
+    assert resp.status_code == 200
+    data = resp.get_json()
+    assert 'devices' in data
+    assert len(data['devices']) == 1
+    assert data['devices'][0]['type'] == 'rtlsdr'
+    assert data['devices'][0]['name'] == 'Generic RTL2832U'
+
+
+def test_sdr_devices_handles_detection_failure(client):
+    """SDR detection failure returns empty list with error."""
+    _login(client)
+    with patch('utils.sdr.detection.detect_all_devices', side_effect=RuntimeError('no devices')):
+        resp = client.get('/system/sdr_devices')
+    assert resp.status_code == 200
+    data = resp.get_json()
+    assert data['devices'] == []
+    assert 'error' in data
+
+
+def test_stream_returns_sse_content_type(client):
+    """GET /system/stream returns text/event-stream."""
+    _login(client)
+    resp = client.get('/system/stream')
+    assert resp.status_code == 200
+    assert 'text/event-stream' in resp.content_type