Improve light/dark theme toggle

Dockerfile

@@ -19,6 +19,8 @@ RUN apt-get update && apt-get upgrade -y \
   && apt-get install --no-install-recommends -y \
     bash \
     curl \
+    nodejs \
+    npm \
   && curl -sSL 'https://install.python-poetry.org' | python - \
   && poetry --version \
   && apt-get purge -y --auto-remove -o APT::AutoRemove::RecommendsImportant=false \
@@ -33,6 +35,12 @@ RUN chown -R timetracker:timetracker /home/timetracker/app
 COPY entrypoint.sh /
 RUN chmod +x /entrypoint.sh
 
+USER timetracker
+
+# Install Node.js dependencies and build Svelte app
+RUN npm install
+RUN npm run build
+
 RUN --mount=type=cache,target="$POETRY_CACHE_DIR" \
     echo "$PROD" \
     && poetry version \