feat(web): add QQ beta-community group to homepage + READMEs

Fills the long-empty "内 测 用 户 群" placeholder (was "群二维码 /
邀请链接（待补充）") on the homepage contact grid with the real QQ
group QR (group ID 575404333) plus a scan-or-search line.

Mirrors it across all three READMEs as a scan-to-join block right
after the contact line, rendered from apps/web/public/qq-group.webp
(760×760 QR-only crop with a white quiet zone, ~45KB).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.ja.md

@@ -33,6 +33,10 @@ InfiPlot は、AI がコンテンツをリアルタイムに生成するイン
 
 お問い合わせ：hi@infiplot.com
 
+**InfiPlot ベータ交流グループ**（QQ グループ番号 `575404333`）—— QR コードを読み取って参加し、フィードバックや共同開発にご参加ください：
+
+<img src="apps/web/public/qq-group.webp" alt="InfiPlot ベータ交流グループ QQ QRコード" width="200" />
+
 ---
 
 ## 仕組み

README.md

@@ -56,6 +56,10 @@ The project is still very early and many features are far from polished. We'd lo
 
 Get in touch: hi@infiplot.com
 
+Scan to join our **beta community on QQ** (group ID `575404333`) to share feedback and help shape the project:
+
+<img src="apps/web/public/qq-group.webp" alt="InfiPlot beta community QQ group QR code" width="200" />
+
 ---
 
 ## How it works

README.zh-CN.md

@@ -55,6 +55,10 @@ InfiPlot是一款AI实时生成内容的互动剧情游戏，这里没有预设
 
 联系方式：hi@infiplot.com
 
+欢迎扫码加入 **InfiPlot 内测交流群**（QQ 群号 `575404333`），一起反馈体验、参与共建：
+
+<img src="apps/web/public/qq-group.webp" alt="InfiPlot 内测交流群 QQ 二维码" width="200" />
+
 ---
 
 ## 工作原理

apps/web/app/page.tsx

@@ -722,8 +722,17 @@ export default function HomePage() {
 
           <div>
             <p className="text-[10px] smallcaps text-clay-500 mb-3">内 测 用 户 群</p>
-            <p className="font-serif italic text-clay-500 text-base leading-relaxed">
-              群二维码 / 邀请链接（待补充）
+            <img
+              src="/qq-group.webp"
+              alt="InfiPlot 内测交流群 QQ 群二维码（群号 575404333）"
+              width={760}
+              height={760}
+              loading="lazy"
+              className="mx-auto mb-3 w-32 max-w-full rounded-sm border border-clay-900/10 shadow-sm shadow-clay-900/5"
+            />
+            <p className="font-serif text-clay-700 text-base leading-relaxed">
+              <i className="fa-brands fa-qq text-[15px] text-clay-500" /> 扫码加入，或搜索群号{" "}
+              <span className="font-sans text-sm text-clay-900">575404333</span>
             </p>
           </div>
         </div>