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_app.cpp

@@ -382,7 +382,7 @@ void EditorApp::processEvents() {
         }
 
         if (event.type == SDL_MOUSEWHEEL && !io.WantCaptureMouse)
-            camera_.processMouseWheel(event.wheel.y);
+            camera_.processMouseWheel(event.wheel.y, (SDL_GetModState() & KMOD_SHIFT) != 0);
     }
 }