Add ephemeral ngrok host workflow

[Oryntai]

Summary

• add npm run host to launch the local relay and an ephemeral ngrok tunnel together
• add npm run join to configure the peer and install MCP in one command
• preserve participant identities across fresh rooms and redact ngrok tokens from errors
• make the no-deploy workflow the default in the English documentation

Verification

• npm ci
• npm run smoke
• npm audit --omit=dev
• invalid-token redaction and relay cleanup check
• git diff --check

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