Added 60dB integration

[manishEMS47]

What we added

A 60db failover layer to the n8n workflow. ElevenLabs stays primary; 60db automatically takes over when an ElevenLabs call errors. Every endpoint returns the same normalized response regardless of which provider answered.

• 4 webhook endpoints: /60db-fo-tts, /60db-fo-tts-stream, /60db-fo-stt, /60db-fo-voices
• ElevenLabs nodes use onError: continueErrorOutput (success → Normalize, error → 60db); a Normalize node gives one consistent
  shape.
• Files: updated Inbound Voice Agent.json, plus 60DB-FAILOVER.md, build-60db-failover.js, and README section.

(Note: fails over speech operations — TTS/STT/voices — not the live phone call, since n8n isn't in the real-time audio path.)

How to use it

1. Import the updated Inbound Voice Agent.json into n8n.
2. Add two HTTP Header Auth credentials on the new nodes: ElevenLabs API (xi-api-key) and 60db API (Authorization: Bearer ).
3. Pass elVoiceId + voiceId60db per request.
4. Activate and call, e.g.:
   curl "https:///webhook/60db-fo-tts?text=Hello&voiceId60db="
5. If ElevenLabs fails, the same-shaped response returns with "provider": "60db".