feat: stats + chat + frontend pages (Stats, Chat, NavBar)

Backend:
- StatsManager.js: JSON persistence, leaderboard, rate-limit 1/5s
- ChatManager.js: 200-msg buffer, JSON persistence
- index.js: routes GET/POST /stats, /chat/history, /chat/send (Zod validation)
- ArenaRoom.js: chat handler broadcasts to room + persists via ChatManager

Unity:
- StatsTracker.cs: distance, maxSpeed, jumps, bumps, checkpoints, raceTime tracking
- ChatUI.cs: F3 toggle, bottom-right panel, polling 3s, unread badge
- NetworkManager.cs: SendChatMessage() + OnMessage<ChatUI.ChatMessage>(chat)
- CheckpointSystem.cs: RegisterCheckpoint/Finish hooks
- PlayerController.cs: RegisterJump/Bump hooks, physics rebalance, billboard fix
- GameHUD.cs: LocalRaceTimer, SetTotalRounds, OnRoundStart signature fix
- GameManager.cs: spectator cam reconnect fix

Frontend:
- NavBar.jsx: fixed top nav, Accueil/Stats/Chat/Jouer
- App.jsx: page state (home/play/stats/chat) + NavBar
- StatsPage.jsx: 6-tab leaderboard, auto-refresh 30s
- ChatPage.jsx: polling 3s, localStorage name, Enter to send

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

game/Assets/PlayerController.cs

@@ -376,9 +376,9 @@ public class PlayerController : MonoBehaviour
     {
         if (context.started)
         {
-            // Touche appuyée
             isJumpPressed = true;
             jumpPressTime = 0f;
+            StatsTracker.Instance?.RegisterJump();
             Debug.Log("Jump Started");
         }
         else if (context.performed)
@@ -516,6 +516,7 @@ public class PlayerController : MonoBehaviour
             return;
 
         _lastBumpTime[id] = Time.time;
+        StatsTracker.Instance?.RegisterBump();
 
         // Repulsion direction: from remote toward local player
         Vector3 dir = (transform.position - other.transform.position).normalized;
@@ -606,6 +607,13 @@ public class PlayerController : MonoBehaviour
             fontStyle = FontStyle.Bold
         };
         labelStyle.normal.textColor = new Color(1f, 1f, 1f, _gaugeDisplayAlpha * 0.9f);
+        // Outline: draw 4× in black at ±1px, then once in white
+        var shadowStyle = new GUIStyle(labelStyle);
+        shadowStyle.normal.textColor = new Color(0f, 0f, 0f, _gaugeDisplayAlpha * 0.55f);
+        GUI.Label(new Rect(x + 1f, y - 25f, barWidth, 24f), "JUMP POWER", shadowStyle);
+        GUI.Label(new Rect(x - 1f, y - 27f, barWidth, 24f), "JUMP POWER", shadowStyle);
+        GUI.Label(new Rect(x + 1f, y - 27f, barWidth, 24f), "JUMP POWER", shadowStyle);
+        GUI.Label(new Rect(x - 1f, y - 25f, barWidth, 24f), "JUMP POWER", shadowStyle);
         GUI.Label(new Rect(x, y - 26f, barWidth, 24f), "JUMP POWER", labelStyle);
 
         // Ensure textures