Improve MCP setup guidance in Settings

[anhtahaylove]

Summary

• keep the downloaded MCP folder visible in Settings after download
• add setup steps for npm install, MCP registration, and SHARDX_TOKEN usage
• add buttons to open the downloaded folder, copy the install command, and copy a token-free MCP config snippet

Validation

• npm run build
• git diff --check -- src/App.tsx src/App.css

Notes

• UI-only change; no backend/API/browser engine/fingerprint behavior changed.
• Config snippet intentionally omits token values and relies on SHARDX_TOKEN from the environment.