chore: update changelog for calendar customization

.changeset/tame-students-tan.md

@@ -0,0 +1,28 @@
+---
+"@nextui-org/calendar": major
+---
+
+### Changes
+- Added support for customizing calendar cells.
+  - You can now use `children` to customize the content of calendar cells.
+  - The default structure of calendar cells has been updated to improve flexibility.
+
+### Breaking Changes
+- **WHAT**: The following changes might affect existing implementations:
+  1. Style class names have been renamed (e.g., `cellButton` → `cellHeader`).
+  2. The internal structure of calendar cells has changed, which may cause existing styles to no longer apply.
+- **WHY**: These changes were made to provide better flexibility and support for modern styling and customization.
+- **HOW**:
+  1. If you are using custom styles, update the class names to the new ones.
+  2. Use `children` to customize the content of calendar cells.
+  3. Refer to the example below for implementation:
+
+```jsx
+<Calendar>
+  {(date) => (
+    <div style={{ backgroundColor: "lightblue" }}>
+      <span>{date.day}</span>
+    </div>
+  )}
+</Calendar>
+```