Reapply "Add Turnstile captcha to login"

This reverts commit a7c732e139.

Dockerfile

@@ -1,6 +1,8 @@
 # Build stage
 FROM node:20-alpine AS build
 WORKDIR /app
+ARG VITE_TURNSTILE_SITE_KEY
+ENV VITE_TURNSTILE_SITE_KEY=$VITE_TURNSTILE_SITE_KEY
 COPY package*.json ./
 RUN npm install
 COPY . .
@@ -11,4 +13,4 @@ FROM nginx:alpine
 COPY --from=build /app/dist /usr/share/nginx/html
 COPY nginx.conf /etc/nginx/conf.d/default.conf
 EXPOSE 80
-CMD ["nginx", "-g", "daemon off;"]
+CMD ["nginx", "-g", "daemon off;"]