backend/apps/dashboard_layout/ was never mounted in main.py and had no
frontend/electron callers — its SubApp and endpoints were fully superseded
by backend/apps/dashboards/. backend/apps/service/models.py was an empty
placeholder with no importers. Also adds .dead-code-scan/ and the scan
script to .gitignore, and drops the stale dashboard_layout/ entry from
the README directory tree.
Co-authored-by: Cursor <cursoragent@cursor.com>
