Add Side Panel to Lab

.changeset/sweet-snails-sneeze.md

@@ -0,0 +1,16 @@
+---
+"@salt-ds/lab": minor
+---
+
+Added `SidePanel`.
+
+`SidePanel` is a collapsible container that slides in from an edge of its parent, providing supplementary content or controls without disrupting the main layout.
+
+```tsx
+<SidePanelGroup>
+  <SidePanelTrigger />
+  <SidePanel>
+    <SidePanelCloseTrigger />
+  </SidePanel>
+</SidePanelGroup>
+```