Update CLOUDFLARE_WORKER_URL in acontext-cli

[ultranity]

update CLOUDFLARE_WORKER_URL to use environment variable or host.docker.internal

Why we need this PR?

Failed to create sandbox when start server with acontext server up:
APIError: 500: failed to create sandbox

Describe your solution

CLOUDFLARE_WORKER_URL is no longer hardcoded to localhost:8787, which is not available for acontext-server-core in docker

Impact Areas

Which part of Acontext would this feature affect?

• Client SDK (Python)
• Client SDK (TypeScript)
• Core Service
• API Server
• Dashboard
• CLI Tool
• Documentation
• Other: ...

Checklist

• Open your pull request against the dev branch.
• All tests pass in available continuous integration systems (e.g., GitHub Actions).
• Tests are added or modified as needed to cover code changes.

[GenerQAQ]

LGTM

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