Double-gated install: only loads when DEBUG=true AND USE_SQLITE=true,
never in prod. Lets us profile SQL query counts on the dashboard and
payroll pages before attacking N+1 hotspots.
requirements.txt adds django-debug-toolbar==6.0.0
config/settings.py conditionally appends to INSTALLED_APPS + MIDDLEWARE
config/urls.py conditionally includes __debug__ route
No behavioural change to production.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
