Add @langchain/core dependency and update imports***

***Update SidepanelRouting to use dark mode***
***Add image support to PlaygroundMessage component

src/libs/to-base64.ts

@@ -0,0 +1,7 @@
+export const toBase64 = (file: File) =>
+  new Promise<string>((resolve, reject) => {
+    const reader = new FileReader()
+    reader.readAsDataURL(file)
+    reader.onload = () => resolve(reader.result as string)
+    reader.onerror = (error) => reject(error)
+  })