Add a Plivo telephony example

[sarveshpatil-plivo]

What

Currently voice-examples/agent/telephony/ has one example, xai/, a Grok-native integration over Twilio Media Streams. We'd like to add a second telephony provider, Plivo, as a sibling example.

Proposed structure

We'd suggest grouping by provider under xai/, moving the current example into xai/twilio/ and adding xai/plivo/ alongside it:

voice-examples/agent/telephony/
  xai/
    twilio/    (the current xai/ example)
    plivo/     (new)

It keeps the examples consistent as more providers are added, and shows Grok working across different telephony providers.

Why

Grok realtime uses mu-law 8 kHz audio (audio/pcmu). Plivo Audio Streaming is also mu-law 8 kHz, so the bridge forwards audio both ways with no transcoding or resampling, a minimal and easy-to-follow example. It also shows the realtime pattern isn't tied to a single telephony provider.

What the Plivo example covers

Mirrors the existing xai/ example:

• Node and TypeScript, Express with express-ws
• Inbound calls (answer webhook + media stream) and outbound calls
• Bidirectional mu-law 8 kHz passthrough between Plivo and Grok realtime
• Barge-in, i.e. bot audio is cleared when the caller starts speaking

Additional functionality:

• A sample tool call (end the call)
• Startup auto-provisioning that points a Plivo application at the server webhooks

The Plivo example is complete and verified end to end against a live Plivo account — inbound call, outbound call, barge-in, and the end-call tool all work. Ready to open the PR once you let us know the structure you'd prefer, and we're happy to match it.