feat: Implement door interaction system and UI improvements

- Add interactive door system with click detection on door meshes
- Create custom DoorModal component replacing browser confirm()
- Implement door opening with texture change to door1_open.png
- Add additive door rendering to preserve opened doors
- Remove exploration button and requestExploration method
- Implement camera orbit controls with smooth animations
- Add active view indicator (yellow highlight) on camera buttons
- Add vertical zoom slider with label
- Fix camera to maintain isometric perspective while rotating
- Integrate all systems into main game loop

src/engine/game/Entity.js

@@ -0,0 +1,20 @@
+
+export class Entity {
+    constructor(id, name, type, x, y, texturePath) {
+        this.id = id;
+        this.name = name;
+        this.type = type; // 'hero', 'monster'
+        this.x = x;
+        this.y = y;
+        this.texturePath = texturePath;
+        this.stats = {
+            move: 4,
+            wounds: 10
+        };
+    }
+
+    setPosition(x, y) {
+        this.x = x;
+        this.y = y;
+    }
+}