Save to Google Docs

Press Save to Google Docs in the toolbar to upload the current lesson straight to the signed-in user's Google Drive as an editable Google Doc. The flow is entirely client-side:

1. Google Identity Services issues a short-lived OAuth2 access token, prompting the user to sign in and consent the first time.
2. The app builds the same docx as Export DOCX, then uploads it to the Drive files endpoint as multipart/related, asking Drive to store it as application/vnd.google-apps.document so it is converted to a Google Doc.
3. On success a toast offers an Open link to the new doc.

The app requests only the drive.file scope, so it can touch only the files it creates — never the user's existing Drive contents. The button is hidden unless VITE_GOOGLE_CLIENT_ID is set (see Environment variables). The OAuth client must list every origin the app is served from (e.g. http://localhost:5173 and the production URL) under Authorised JavaScript origins, and the Google Drive API must be enabled for the project.