Fix start-dev.sh: Backend failed to start due to venv activation issue

- Use venv Python directly instead of trying to activate in background process
- Fix frontend path from '../frontend' to 'frontend'
- Backend now starts correctly with virtualenv dependencies

Author: Rafael Teodoro

start-dev.sh

@@ -63,12 +63,12 @@ cd ..
 
 echo "🚀 Starting Backend on http://localhost:8000..."
 cd backend
-source venv/bin/activate
-python main.py &
+./venv/bin/python main.py &
 BACKEND_PID=$!
+cd ..
 
 echo "🚀 Starting Frontend on http://localhost:3000..."
-cd ../frontend
+cd frontend
 npm run dev &
 FRONTEND_PID=$!