build: configure UTF-8 locale in devcontainer (#195)

Author: stainless-app[bot]

.devcontainer/Dockerfile

@@ -14,6 +14,10 @@ RUN apt-get update && apt-get install -y \
   vim \
   && apt-get clean autoclean
 
+# Ensure UTF-8 encoding
+ENV LANG=C.UTF-8
+ENV LC_ALL=C.UTF-8
+
 WORKDIR /workspace
 
 COPY . /workspace