Get aggregated dashboard metrics for admin panel

{
    "isSuccess": true,
    "statusCode": 200,
    "data": {
        "generatedAt": "2026-02-14T08:21:20.120Z",
        "months": 6,
        "overview": {
            "users": {
                "total": 1500,
                "admins": 15,
                "registrationCompleted": 1280,
                "completionRate": 85.33,
                "newLast30Days": 54,
                "monthlyGrowthRate": 8.2
            },
            "courses": {
                "total": 42
            },
            "tests": {
                "totalTests": 28,
                "totalSubmissions": 2048,
                "averageScore": 71.2,
                "submissionsLast30Days": 176,
                "monthlyGrowthRate": 6.5
            },
            "contacts": {
                "total": 340,
                "pending": 58,
                "replied": 282,
                "replyRate": 82.94,
                "newLast30Days": 23
            },
            "materials": {
                "total": 60,
                "assignments": 812,
                "assignedUsers": 403,
                "avgAssignmentsPerUser": 2.01,
                "assignmentsLast30Days": 91
            }
        },
        "trends": [
            {
                "month": "2026-02",
                "label": "Feb 2026",
                "users": 120,
                "testSubmissions": 87,
                "contacts": 16,
                "materialAssignments": 43
            }
        ],
        "distributions": {
            "roles": [
                {
                    "key": "user",
                    "label": "User",
                    "count": 42,
                    "percentage": 66.67
                }
            ],
            "contactsByStatus": [
                {
                    "key": "user",
                    "label": "User",
                    "count": 42,
                    "percentage": 66.67
                }
            ],
            "levels": [
                {
                    "key": "user",
                    "label": "User",
                    "count": 42,
                    "percentage": 66.67,
                    "averageScore": 72.5
                }
            ],
            "languages": [
                {
                    "key": "en",
                    "label": "EN",
                    "submissions": 124,
                    "averageScore": 69.2
                }
            ]
        },
        "recentActivity": {
            "contacts": [
                {
                    "id": "67aeef90b2c7d32d4f6f4f11",
                    "fullName": "John Doe",
                    "email": "john@example.com",
                    "status": "PENDING",
                    "createdAt": "2026-02-14T08:21:20.120Z",
                    "repliedAt": "2026-02-14T08:45:10.903Z",
                    "source": "instagram"
                }
            ],
            "testResults": [
                {
                    "id": "67aeef90b2c7d32d4f6f4f12",
                    "userName": "John Doe",
                    "userEmail": "john@example.com",
                    "level": "B2",
                    "totalScore": 78,
                    "targetLanguage": "en",
                    "testTitle": "English Placement Test",
                    "completedAt": "2026-02-14T08:21:20.120Z"
                }
            ]
        }
    },
    "errors": [
        "Error messages..."
    ],
    "timestamp": "2026-02-14T09:58:22.138Z"
}