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/README.md

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+# FlatRender — Coming Soon landing
+
+A **single, self-contained HTML page** (no build step, no app dependencies) packaged as
+a tiny nginx Docker image. RTL Persian, matches the FlatRender brand (blue + Vazirmatn +
+LogoMark), with a **live countdown to ۱ تیر ۱۴۰۵ (1 Tir 1405 = 22 June 2026, Iran time)**.
+
+## Run
+
+```bash
+docker build -t flatrender-coming-soon ./coming-soon
+docker run -d -p 8090:80 --name flatrender-coming-soon flatrender-coming-soon
+# → http://localhost:8090
+```
+
+Or just open `index.html` directly in a browser — it works with zero server.
+
+## What it includes
+
+- Animated brand-gradient background + grid overlay
+- LogoMark + Persian wordmark (فلت‌رندر)
+- Headline + lead reflecting the app's value (AI video & image maker)
+- Live countdown (days / hours / minutes / seconds) in Persian digits
+- Feature chips mirroring the app: video maker, image editor, 1200+ templates,
+  music & voiceover, HD/4K export
+- "Notify me" email capture (posts to `/subscribe` if a backend is wired; otherwise
+  shows a thank-you locally)
+
+## Change the launch date
+
+Edit one line in `index.html`:
+
+```js
+var TARGET = new Date("2026-06-22T00:00:00+03:30").getTime();
+```