index.html modification for external integrations like adsense

Index.html gets overwritten on publish by base44, so no odifications made to index.html on repo gets to final release. You can include lines via panel/code that last to the release, but when the agent tries to do it all changes are lost or faced by errors. Agent should be aware of this and guide the user on how to do, instead of trying and failing everytime he tries to do it.