Add dTelecom action provider for decentralized voice services (#982)

* Add dTelecom action provider and voice agent example

- New dTelecom action provider with 12 actions for decentralized voice
  services (WebRTC, STT, TTS) using x402 micropayments
- Voice agent example using AgentKit + dTelecom agents-js
- Protocol logo added to root README

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Address review feedback: error handling, ReAct agent example, README

- Add try/catch error handling to all 12 action provider methods
- Rewrite voice agent example with LangChain ReAct agent and custom
  AgentKitLLM adapter (replaces hardcoded OpenAILLM)
- Add walletActionProvider and erc20ActionProvider to example
- Add dTelecom to agentkit README action providers table
- Remove unused deps (server-sdk-js, server-sdk-node)
- Change dotenv.config path to default, changeset minor to patch
- Update example README with new architecture docs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* Fix lint: add missing JSDoc param/returns to getErrorMessage

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>