feat(editor): scroll wheel zoom, clickable minimap navigation

- Scroll wheel now zooms camera (moves along look direction) instead
  of adjusting speed. Much more intuitive for terrain editing.
- Shift+scroll adjusts camera speed (old behavior preserved)
- Click on minimap to teleport camera to that location on the terrain
- Zoom speed scales with current camera speed for consistent feel

tools/editor/editor_camera.hpp

@@ -13,7 +13,7 @@ public:
 
     void update(float deltaTime);
     void processMouseMotion(int dx, int dy);
-    void processMouseWheel(float delta);
+    void processMouseWheel(float delta, bool shiftHeld);
     void processKeyEvent(const SDL_KeyboardEvent& event);
     void processMouseButton(const SDL_MouseButtonEvent& event);