fix: resolve test failures blocking CI pipeline (OPC mock, route ordering, system stats)

- Add agent fetchrow to OPC mock to fix "Task or agent not found" errors
- Reorder conversation tracker routes: /search, /stats, /trigger before /{session_id}
- Fix test_task_creator_tracked_in_metadata to expect token username (testuser)
- Mock shutil/psutil in system stats test for non-Synology environments

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

dashboard/backend/tests/integration/test_system.py

@@ -1,11 +1,29 @@
 """Integration tests for system router"""
 
 import pytest
+from unittest.mock import Mock, patch
 
 
 def test_system_stats_endpoint(test_app, admin_headers):
     """Test system stats endpoint returns expected format"""
-    response = test_app.get("/api/system/stats", headers=admin_headers)
+    mock_disk = Mock()
+    mock_disk.total = 1000000000000
+    mock_disk.used = 500000000000
+    mock_disk.free = 500000000000
+
+    mock_mem = Mock()
+    mock_mem.total = 8000000000
+    mock_mem.available = 4000000000
+    mock_mem.used = 4000000000
+    mock_mem.percent = 50.0
+
+    with patch("shutil.disk_usage", return_value=mock_disk), \
+         patch("psutil.disk_partitions", return_value=[]), \
+         patch("psutil.virtual_memory", return_value=mock_mem), \
+         patch("psutil.cpu_percent", return_value=25.5), \
+         patch("psutil.getloadavg", return_value=(1.0, 0.5, 0.2)), \
+         patch("psutil.boot_time", return_value=1000000.0):
+        response = test_app.get("/api/system/stats", headers=admin_headers)
     assert response.status_code == 200
     data = response.json()
     assert "cpu_percent" in data