Add Snell script with Sub-Store JSON output

scripts/snell-README.md

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+# Snell.sh Mango fork
+
+Based on upstream `https://raw.githubusercontent.com/xOS/Snell/master/Snell.sh` fetched 2026-07-05.
+
+Changes:
+- `viewConfig` still prints Surge config.
+- Adds Mihomo/Nikki JSON node output for Snell v1-v5, compatible with Sub-Store JSON input/output.
+- For Snell v6, prints a warning instead of invalid Mihomo config because current MetaCubeX docs only list Snell v1/2/3/4/5 support.
+- `updateShell` can be pointed at your own raw script URL using environment variables:
+  - `SNELL_SCRIPT_URL=https://gitea.example.com/user/repo/raw/branch/main/Snell.sh`
+  - `SNELL_SCRIPT_CN_URL=https://gitea.example.com/user/repo/raw/branch/main/Snell.sh`
+
+Install example after publishing to Gitea:
+
+```bash
+wget -O snell.sh --no-check-certificate https://YOUR-GITEA/user/repo/raw/branch/main/Snell.sh && chmod +x snell.sh && ./snell.sh
+```
+
+Example Mihomo/Sub-Store JSON node:
+
+```json
+{"name":"vps","server":"1.2.3.4","port":2345,"psk":"secret","version":5,"reuse":true,"tfo":true,"type":"snell"}
+```