feat: standalone "Coming Soon" landing (single HTML, dockerized)

RTL Persian landing matching the FlatRender brand (blue + LogoMark), with a live
countdown to ۱ تیر ۱۴۰۵ (1 Tir 1405 = 22 Jun 2026, Iran time), feature chips, and a
notify-me capture. One static index.html served by nginx (coming-soon/Dockerfile);
stack-agnostic, no app dependencies.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

coming-soon/Dockerfile

@@ -0,0 +1,16 @@
+# Standalone "Coming Soon" landing — a single static HTML page served by nginx.
+# Stack-agnostic: build & run anywhere, no app dependencies.
+#
+#   docker build -t flatrender-coming-soon ./coming-soon
+#   docker run -d -p 8090:80 --name flatrender-coming-soon flatrender-coming-soon
+#   → http://localhost:8090
+FROM nginx:1.27-alpine
+
+# Single-page site: replace the default nginx root with our one HTML file.
+RUN rm -f /usr/share/nginx/html/*
+COPY index.html /usr/share/nginx/html/index.html
+
+# Serve index.html for every path (so deep links still land on the page).
+RUN printf 'server {\n  listen 80;\n  root /usr/share/nginx/html;\n  location / {\n    try_files $uri /index.html;\n  }\n}\n' > /etc/nginx/conf.d/default.conf
+
+EXPOSE 80