feat: update dashboard port from 8080 to 8420 in configuration and documentation

Dockerfile

@@ -12,7 +12,7 @@ RUN pip install --no-cache-dir -r requirements.txt
 COPY . .
 
 # Dashboard (Flask) port
-EXPOSE 8080
+EXPOSE 8420
 
 # Create a non-root user
 RUN addgroup -S appgroup && adduser -S appuser -G appgroup