feat: add CI/CD pipeline with Docker + Nginx

- Add Gitea Actions workflow for auto-deploy on push to main
- Add Dockerfile (nginx:alpine based, with layer caching)
- Add nginx.conf (gzip, autoindex, static caching)
- Add .dockerignore
- Migrate cache.html → cache/index.html for directory-based routing

Dockerfile

@@ -0,0 +1,18 @@
+FROM nginx:alpine
+
+# Copy nginx config first (changes less often → cached layer)
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+
+# Copy site content
+COPY . /usr/share/nginx/html/
+
+# Remove non-web files from the image
+RUN rm -rf /usr/share/nginx/html/.git \
+           /usr/share/nginx/html/.gitea \
+           /usr/share/nginx/html/.dockerignore \
+           /usr/share/nginx/html/Dockerfile \
+           /usr/share/nginx/html/LICENSE \
+           /usr/share/nginx/html/README.md
+
+EXPOSE 80
+CMD ["nginx", "-g", "daemon off;"]