refactor: update Docker configuration & docs

- Modified docker-compose.yml to clarify that the server runs as a non-root user.
- Updated Dockerfile to use ARG for VITE_SERVER_URL, allowing build-time overrides.
- Replaced inline Nginx configuration with a separate nginx.conf file for better maintainability.
- Adjusted documentation to reflect changes in Docker setup and troubleshooting steps.

apps/ui/Dockerfile

@@ -23,8 +23,10 @@ COPY apps/ui ./apps/ui
 # Build for web (skip electron)
 # VITE_SERVER_URL tells the UI where to find the API server
 # Using localhost:3008 since both containers expose ports to the host
+# Use ARG to allow overriding at build time: --build-arg VITE_SERVER_URL=http://api.example.com
+ARG VITE_SERVER_URL=http://localhost:3008
 ENV VITE_SKIP_ELECTRON=true
-ENV VITE_SERVER_URL=http://localhost:3008
+ENV VITE_SERVER_URL=${VITE_SERVER_URL}
 RUN npm run build --workspace=apps/ui
 
 # Production stage - serve with nginx
@@ -34,15 +36,7 @@ FROM nginx:alpine
 COPY --from=builder /app/apps/ui/dist /usr/share/nginx/html
 
 # Copy nginx config for SPA routing
-RUN echo 'server { \
-    listen 80; \
-    server_name localhost; \
-    root /usr/share/nginx/html; \
-    index index.html; \
-    location / { \
-        try_files $uri $uri/ /index.html; \
-    } \
-}' > /etc/nginx/conf.d/default.conf
+COPY apps/ui/nginx.conf /etc/nginx/conf.d/default.conf
 
 EXPOSE 80