Dev server crashes when using `make run-local` due to missing files

[vishwa-radhya]

Description

When running the development server using:

make build-local
DEFAULT_DOMAIN=learn-js.org make run-local

the server crashes due to missing files like Welcome.md.

Observations

• The issue occurs when using the Makefile setup
• Running manually via:
  python main.py
  works after adding safeguards

Cause

The code assumes certain files exist (e.g., Welcome.md), but they may be missing for some languages.

Fix

• Add checks before removing files from lists
• Handle missing tutorial files