Containerize for independent deployment

Adds a Dockerfile, nginx config, docker-compose.yml, and a Gitea Actions
workflow (mirroring goonk's), so rack builds and ships as its own image
rather than being embedded in goonk-cv's build - deploys stay fully
decoupled. Targets a subdomain, not a goonk.se subpath, to avoid needing
path-prefix rewriting kept in sync across the build, edge proxy, and
container.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,13 @@
+# Build static site
+FROM node:24-alpine AS build
+WORKDIR /app
+COPY package.json package-lock.json* ./
+RUN npm ci || npm install
+COPY . .
+RUN npm run build
+
+# Serve static output
+FROM nginx:alpine
+COPY --from=build /app/dist/ /usr/share/nginx/html/
+COPY nginx/default.conf /etc/nginx/conf.d/default.conf
+EXPOSE 80