build: add NOINDEX argument for libghostty-vt docs

src/build/docker/lib-c-docs/Dockerfile

@@ -2,6 +2,9 @@
 # Generate documentation with Doxygen
 #--------------------------------------------------------------------
 FROM ubuntu:24.04 AS builder
+
+# Build argument for noindex header
+ARG ADD_NOINDEX_HEADER=false
 RUN apt-get update && apt-get install -y \
     doxygen \
     graphviz \
@@ -16,6 +19,36 @@ RUN doxygen
 # Host the static HTML
 #--------------------------------------------------------------------
 FROM nginx:alpine AS runtime
+
+# Pass build arg to runtime stage
+ARG ADD_NOINDEX_HEADER=false
+ENV ADD_NOINDEX_HEADER=$ADD_NOINDEX_HEADER
+
+# Copy documentation
 COPY --from=builder /ghostty/zig-out/share/ghostty/doc/libghostty /usr/share/nginx/html
+
+# Create entrypoint script
+RUN cat > /entrypoint.sh << 'EOF'
+#!/bin/sh
+if [ "$ADD_NOINDEX_HEADER" = "true" ]; then
+    cat > /etc/nginx/conf.d/noindex.conf << 'INNER_EOF'
+server {
+    listen 80;
+    location / {
+        root /usr/share/nginx/html;
+        index index.html;
+        add_header X-Robots-Tag "noindex, nofollow" always;
+    }
+}
+INNER_EOF
+
+    # Remove default server config
+    rm -f /etc/nginx/conf.d/default.conf
+fi
+exec nginx -g "daemon off;"
+EOF
+
+RUN chmod +x /entrypoint.sh
+
 EXPOSE 80
-CMD ["nginx", "-g", "daemon off;"]
+CMD ["/entrypoint.sh"]