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/conftest.py

@@ -277,7 +277,7 @@ def _patch_opc_db():
     def _make_task(title, description, status, priority, project_id,
                    assigned_to, assigned_type, tags, due_date):
         tid = _next_id(_task_counter)
-        now = datetime.utcnow().isoformat()
+        now = datetime.utcnow()
         task = {
             "id": tid,
             "title": title,
@@ -292,7 +292,7 @@ def _patch_opc_db():
             "created_at": now,
             "updated_at": now,
             "completed_at": None,
-            "due_date": due_date.isoformat() if due_date else None,
+            "due_date": due_date,
         }
         _tasks[tid] = task
         return task
@@ -316,7 +316,7 @@ def _patch_opc_db():
                 return _DictRow(task)
             elif query_lower.startswith("insert into agent_executions"):
                 eid = _next_id(_exec_counter)
-                now = datetime.utcnow().isoformat()
+                now = datetime.utcnow()
                 exec_data = {
                     "id": eid,
                     "task_id": params[0] if len(params) > 0 else None,
@@ -343,6 +343,21 @@ def _patch_opc_db():
                 if tid in _tasks:
                     return _DictRow(_tasks[tid])
                 return None
+            elif query_lower.startswith("select * from agents where id ="):
+                agent_id = params[0] if params else None
+                agents_map = {
+                    "pm": {"id": "pm", "name": "Project Manager", "role": "PM",
+                           "description": "test", "capabilities": "[]", "system_prompt": "test",
+                           "config": '{"approval_level":"auto"}', "enabled": True,
+                           "created_at": datetime.utcnow().isoformat()},
+                    "cto": {"id": "cto", "name": "CTO", "role": "CTO",
+                            "description": "test", "capabilities": "[]", "system_prompt": "test",
+                            "config": '{"approval_level":"cxo"}', "enabled": True,
+                            "created_at": datetime.utcnow().isoformat()},
+                }
+                if agent_id in agents_map:
+                    return _DictRow(agents_map[agent_id])
+                return None
             elif query_lower.startswith("select * from agent_executions where id ="):
                 eid = params[0] if params else None
                 if eid in _executions: