fix: register alien x llm UCEP provider

[saurabhhhcodes]

Closes #1

Summary

• add the missing alien-x-llm UCEP extension provider backed by LLMService
• register the provider at startup so it is advertised through the existing extension registry
• pass the remote peer id into command handlers and document the working terminal startup flow

Validation

• node --check agent-llm.js && node --check llm-extension-provider.js && node --check extension-provider.js && node --check index.js
• npm run build from p2p-X/web
• TIMEOUT_DURATION=3s INTERACTIVE=false npm start from p2p-X/web/app reached Registering extension: alien-x-llm v1.0.0 at /uc/extension/alien-x-llm/1.0.0 and LLM extension registered: alien-x-llm

[saurabhhhcodes]

Hi maintainers, could you please apply the appropriate GSSoC/scoring labels if this PR is eligible? It closes #1, is assigned, merge-clean, and the GitGuardian check is passing. Thanks!

[Nkovaturient]

@saurabhhhcodes : could you screencast and demo the working?