The docs are deployed to Google Firebase hosting via Travis deployment config, which expects firebase.json in the repository root, which is done by a Grunt task (firebaseDocsJsonForTravis) that modifies the paths in the firebase.json and copies it into the repository root.
See travis.yml for the complete deployment config, and scripts/travis/build.sh for the full deployment build steps.
grunt:prepareDeploy. This copies docs content files into deploy/docs and the partials for Search Engine AJAX Crawling into ./functions/content.
firebase serve --only functions,hosting Creates a server at localhost:5000 that serves from deploy/docs and uses the local function
See /scripts/code.angularjs.org-firebase/readme.firebase.code.md for the firebase deployment to code.angularjs.org