HeightMap: add GRID_MAX limit and input validation

Fixes potential integer overflow and invalid input issues:

- Add GRID_MAX constant (8192) to Common.h for global use
- Validate HeightMap dimensions against GRID_MAX to prevent
  integer overflow in w*h calculations (65536*65536 = 0)
- Add min > max validation for clamp() and normalize()
- Add unit tests for all new validation cases

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

src/PyHeightMap.cpp

@@ -102,6 +102,13 @@ int PyHeightMap::init(PyHeightMapObject* self, PyObject* args, PyObject* kwds)
         return -1;
     }
 
+    if (width > GRID_MAX || height > GRID_MAX) {
+        PyErr_Format(PyExc_ValueError,
+            "HeightMap dimensions cannot exceed %d (got %dx%d)",
+            GRID_MAX, width, height);
+        return -1;
+    }
+
     // Clean up any existing heightmap
     if (self->heightmap) {
         TCOD_heightmap_delete(self->heightmap);
@@ -253,6 +260,11 @@ PyObject* PyHeightMap::clamp(PyHeightMapObject* self, PyObject* args, PyObject*
         return nullptr;
     }
 
+    if (min_val > max_val) {
+        PyErr_SetString(PyExc_ValueError, "min must be less than or equal to max");
+        return nullptr;
+    }
+
     TCOD_heightmap_clamp(self->heightmap, min_val, max_val);
 
     // Return self for chaining
@@ -277,6 +289,11 @@ PyObject* PyHeightMap::normalize(PyHeightMapObject* self, PyObject* args, PyObje
         return nullptr;
     }
 
+    if (min_val > max_val) {
+        PyErr_SetString(PyExc_ValueError, "min must be less than or equal to max");
+        return nullptr;
+    }
+
     TCOD_heightmap_normalize(self->heightmap, min_val, max_val);
 
     // Return self for chaining