CI: speed up build

Dockerfile

@@ -0,0 +1,24 @@
+# --- Stage 1: Build & Test ---
+FROM ruby:3.3 AS builder
+
+# Instalace závislostí pro html-proofer (pokud jsou potřeba)
+RUN apt-get update && apt-get install -y build-essential
+
+WORKDIR /srv/jekyll
+COPY Gemfile* ./
+RUN bundle install
+
+COPY . .
+
+# Samotný build webu
+RUN JEKYLL_ENV=production bundle exec jekyll build
+
+# TEST: Pokud htmlproofer skončí chybou, celý Docker build selže
+RUN bundle exec htmlproofer ./_site \
+    --disable-external \
+    --ignore-urls "/^http:\/\/127.0.0.1/,/^http:\/\/0.0.0.0/,/^http:\/\/localhost/"
+
+# --- Stage 2: Final Image ---
+FROM nginx:alpine
+COPY --from=builder /srv/jekyll/_site /usr/share/nginx/html
+EXPOSE 80