Grid: add apply_threshold and apply_ranges for HeightMap (closes #199)

Add methods to apply HeightMap data to Grid walkable/transparent properties:
- apply_threshold(source, range, walkable, transparent): Apply properties
  to cells where HeightMap value is in the specified range
- apply_ranges(source, ranges): Apply multiple threshold rules in one pass

Features:
- Size mismatch between HeightMap and Grid raises ValueError
- Both methods return self for chaining
- Uses dynamic type lookup via module for HeightMap type checking
- First matching range wins in apply_ranges
- Cells not matching any range remain unchanged
- TCOD map is synced after changes for FOV/pathfinding

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/UIGrid.h

@@ -179,6 +179,10 @@ public:
     static PyObject* py_entities_in_radius(PyUIGridObject* self, PyObject* args, PyObject* kwds);  // #115
     static PyObject* py_center_camera(PyUIGridObject* self, PyObject* args);  // #169
 
+    // #199 - HeightMap application methods
+    static PyObject* py_apply_threshold(PyUIGridObject* self, PyObject* args, PyObject* kwds);
+    static PyObject* py_apply_ranges(PyUIGridObject* self, PyObject* args);
+
     // #169 - Camera positioning
     void center_camera();  // Center on grid's middle tile
     void center_camera(float tile_x, float tile_y);  // Center on specific tile