feat: add BT_level1 and new overlay types (cell, wsmi)

Add new level BT_level1.json featuring guards, enemies, and interactive elements.
Introduce "cell" and "wsmi" overlay configurations in src/config/overlays.json.
Update overlay textures (overlays.png, overlays.psd) to support the new overlay frames.

src/config/overlays.json

@@ -20,6 +20,20 @@
       "color": "#3f8f3f",
       "texture": "assets/textures/overlays.png",
       "frame": 2
+    },
+    {
+      "id": "cell",
+      "name": "Cell",
+      "color": "#3f8f3f",
+      "texture": "assets/textures/overlays.png",
+      "frame": 3
+    },
+    {
+      "id": "wsmi",
+      "name": "Science Meets",
+      "color": "#3f8f3f",
+      "texture": "assets/textures/overlays.png",
+      "frame": 4
     }
   ]
 }