feat: Adds robust speed hack detection and movement throttling (#2266)

## Summary

   Server-side movement throttle that prevents speed hacking while accurately identifying cheaters with detection of lagging connections.

   **Key features:**
   - Credit buffer (200ms) absorbs timing jitter from legitimate players
   - Movement queue handles larger bursts, draining at proper game-tick intervals
   - RTT measurement distinguishes network lag from speed hacks
   - Queue depth detection catches ACK-throttled speed hacks (going straight)

   ## How It Works

   **Throttle** (prevention): Movements arriving too early either consume credit or get queued. The queue drains at
   correct intervals, so speed hackers can't move faster regardless of what they send.

   **Detection** (identification): Combines multiple signals to identify cheaters:
   | Signal | What it catches |
   |--------|-----------------|
   | Queue depth ≥4 sustained | ACK-throttled speed hacks (client limits unacked moves to 5) |
   | Movement rate >1.05x | Direction-change speed hacks where timing is visible |
   | Stable RTT + high queue | Eliminates false positives from laggy players |

   **RTT-Aware Logic:**
   - Probes only sent to players actively moving (event-driven, not global loop)
   - Stable low-latency + problems = suspicious
   - Unstable/high-latency + problems = probably just lag, throttle handles it

   ## Configuration

   ```json
   {
     "movementThrottle.maxCredit": 200,
     "movementThrottle.softQueueLimit": 6,
     "movementThrottle.hardQueueLimit": 10,
     "movementThrottle.debugLogging": false
   }
   ```

Projects/Server/Network/NetState/NetState.cs

@@ -63,9 +63,9 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
     // Managed socket with buffers (handles lifecycle automatically)
     internal RingSocket _socket;
 
-    // Speed Hack Prevention
-    internal long _movementCredit;
-    internal long _nextMovementTime;
+    // General packet throttle state (used for other throttled packets)
+    internal bool _isThrottled;
+
     private IAccount _account;
 
     internal enum ParserState
@@ -942,6 +942,14 @@ public partial class NetState : IComparable<NetState>, IValueLinkListNode<NetSta
         }
         else
         {
+            // Authenticated pre-game clients (login screens): send keep-alive instead of disconnecting.
+            // The 0xBD ClientVersionRequest resets NextActivityCheck via DataSent.
+            if (_account != null && Mobile == null)
+            {
+                this.SendClientVersionRequest();
+                return;
+            }
+
             LogInfo("Disconnecting due to inactivity...");
             Disconnect("Disconnecting due to inactivity.");
         }