Docs: replace broken chatbot Spaces links in guides

[monkeyjack123]

Summary

Replaces outdated/broken Hugging Face Spaces links in the custom chatbot guides with maintained, working Gradio demo Spaces.

Changes

• Updated related Spaces metadata link in English guide
• Updated end-of-guide example links in English guide
• Mirrored the same link updates in the Chinese guide

Validation

• Checked updated target Spaces return HTTP 200

Fixes #12838

[gradio-pr-bot]

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[gradio-pr-bot]

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• Docs: replace broken chatbot Spaces links in guides

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✅ Changeset approved by @freddyaboulton

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