[Feature]: IVR/calling-agent for non-smartphone voters

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Issue Description ✍️

Description: Implement a calling agent flow (IVR) under the chatbot directory to allow voters to call a number, verify identity (OTP), and cast/confirm vote. Store verification results off-chain; anchor a proof (e.g., a signed message or Merkle root) on-chain to prevent tampering.

Why: Inclusive voting for users without smartphones. The repo already has a chatbot folder to extend.

### Record

- [x] I have synced all my node versions as mentioned in the project
- [x] I am using the same version of npm as is the project
- [x] My current branch is in sync with the development branch
- [x] I want to work on this issue