Update CHANGES.md.

Author: kring

CHANGES.md

@@ -1,5 +1,18 @@
 # Change Log
 
+### ? - ?
+
+##### Breaking Changes :mega:
+
+- `Tileset::getRootTile` now only provides a const pointer to the root `Tile`, even when called on a non-const `Tileset`. Most modifications tile tile instances owned by the tileset would be unsafe.
+- The `slowlyGetCurrentStates` and `slowlyGetPreviousStates` methods of `TreeTraversalState` now return the state map with a raw pointer to a constant node as the key, even if the node pointer type is a smart pointer.
+- `DebugTileStateDatabase::recordTileState` now expects the states to be provided as `std::unordered_map<const Tile*, TileSelectionState>` instead of `std::unordered_map<IntrusivePointer<Tile>, TileSelectionState>`.
+
+##### Additions :tada:
+
+- Added `element_type` to `IntrusivePointer`, allowing it to be used with `std::pointer_types`.
+- Added implicit conversion of `IntrusivePointer<T>` to `T*`.
+
 ### v0.50.0 - 2025-08-01
 
 ##### Breaking Changes :mega: