Check for and improve accessibility issues

- [ ] Solve the "Add a 'onKeyPress|onKeyDown|onKeyUp' attribute to this tag" sonar qube issue
- in editor templates `openExistingProjectModal.html` and `navbar.html` and project template `projects.html`
- I have marked this issue as accepted on sonar for now (see https://sonarcloud.io/project/issues?issueStatuses=ACCEPTED&id=ARTIST-Association_CANVAS)
- [ ] Check for other accessibility features we should include

Start by reviewing the accessibility warning in SonarCloud, then inspect the links in editor templates openExistingProjectModal.html and navbar.html and the project template projects.html. Resolve the named keyboard-handler issue and assess the other accessibility features requested; done means the listed warning and any agreed additional findings are addressed.

Written by the indexing model from the issue text.