Implement telemetry system with data collection and reporting

Signed-off-by: Dmitrii <computer@yawaflua.tech>

Took 20 minutes

backend/SpMega.Backend/Controllers/v1/TelemetryController.cs

@@ -0,0 +1,45 @@
+using System.Diagnostics;
+using System.Text.Json;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using SpMega.Backend.Persistent.Models.DTO;
+using SpMega.Backend.Persistent.Models.Users;
+
+namespace SpMega.Backend.Controllers.v1;
+
+[ApiController]
+[Route("api/v1/telemetry")]
+public class TelemetryController : ControllerBase
+{
+    private static readonly ActivitySource Source = new("SpMega.ModTelemetry");
+
+    [HttpPost]
+    [Authorize]
+    public IActionResult Post([FromBody] ModTelemetryBatchDto batch)
+    {
+        if (batch?.Events == null || batch.Events.Count == 0)
+        {
+            return Ok(new { received = 0 });
+        }
+
+        var user = HttpContext.Items["@me"] as User;
+        var userId = user?.Id.ToString() ?? User.FindFirst(System.Security.Claims.ClaimTypes.NameIdentifier)?.Value ?? "anonymous";
+        var sessionId = !string.IsNullOrEmpty(batch.SessionId) ? batch.SessionId : Guid.NewGuid().ToString("N");
+
+        foreach (var e in batch.Events)
+        {
+            using var activity = Source.StartActivity("mod.telemetry.event", ActivityKind.Internal);
+            if (activity is null) continue;
+
+            activity.SetTag("user.id", userId);
+            activity.SetTag("session.id", sessionId);
+            activity.SetTag("client.version", batch.ClientVersion ?? string.Empty);
+            activity.SetTag("event.type", e.EventType);
+            activity.SetTag("event.timestamp", e.Timestamp.ToString("O"));
+            activity.SetTag("event.payload", JsonSerializer.Serialize(e.Payload));
+            activity.SetTag("batch.sent_at", batch.SentAt.ToString("O"));
+        }
+
+        return Ok(new { received = batch.Events.Count });
+    }
+}