Rename widget.md to chat-widget.md

- The code changes renamed the file `widget.mdx` to `chat-widget.mdx`.
- The content has been modified to reflect the new name and provide a more detailed description of the Langflow Chat Widget.
- The usage instructions have been updated to reflect the changes.

This commit renames `widget.mdx` to `chat-widget.mdx` and provides more detailed information about the Langflow Chat Widget, including its features, usage in HTML, React, and Angular, and customization options.

docs/sidebars.js

@@ -21,7 +21,7 @@ module.exports = {
         "guidelines/collection",
         "guidelines/prompt-customization",
         "guidelines/chat-interface",
-        "guidelines/widget",
+        "guidelines/chat-widget",
       ],
     },
     {