feat: embeddable CompanyGame with loader, poster, no-WebGL fallback and SEO

- CompanyGame bundles the store, a branded loader with start-up progress, an optional
  light poster (Enter the game) and a company-info fallback when WebGL is missing.
- startMode prop and ?mode= start straight in a mode; ?poster shows the poster first.
- Pixel ratio capped at 1.5 on touch devices and 1.75 on desktop (constants/graphics.js).
- Build writes the title, description, Organization JSON-LD and a hidden Persian
  summary into index.html from the company config.
- README explains iframe and component embedding.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

vite.config.js

@@ -4,6 +4,7 @@ import { defineConfig } from 'vite';
 import { readdirSync, statSync } from 'node:fs';
 import { join, relative } from 'node:path';
 import { createHash } from 'node:crypto';
+import { seoHead, seoStructuredData, seoSummary } from './src/utils/seoSummary.js';
 
 const listFiles = (dir) =>
   readdirSync(dir).flatMap((name) => {
@@ -62,11 +63,23 @@ self.addEventListener('fetch', event => {
   };
 }
 
+// Writes the company's title, description, structured data and a hidden Persian summary into
+// index.html, so search engines and link previews see real content without running the game.
+function companySeo() {
+  return {
+    name: 'company-seo',
+    transformIndexHtml: (html) =>
+      html
+        .replace('<!--seo-head-->', `${seoHead()}\n    ${seoStructuredData()}`)
+        .replace('<!--seo-summary-->', seoSummary()),
+  };
+}
+
 export default defineConfig({
   // Relative assets also load under a GitHub Pages repository path.
   base: './',
   resolve: { alias: { '@': fileURLToPath(new URL('./src', import.meta.url)) } },
-  plugins: [react(), offlineServiceWorker()],
+  plugins: [react(), companySeo(), offlineServiceWorker()],
   // Top-level await loads the building and imagery files before the world is built.
   build: { target: 'es2022' },
   server: {