API cleanup

[ethanpalm]

Documentation changes

This PR fixes some inaccuracies in how to find project ID and domain parameters, removes deprecated endpoints, and removes unused endpoints from OpenAPI specs.

• admin-openapi.json
  • Removes hallucinated endpoints
  • Clearer info to find and copy your project ID
• /assistant
  • delete create-topic.mdx
  • delete generate-message.mdx
• discovery-openapi.json
  • Accurate information on where to find {domain}
  • Remove deprecated /chat/topic and /chat/message paths
• docs.json
  • Sentence case API reference group name
• openapi.json
  • Clearer information on how to find {projectId}

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For Reviewers

When reviewing documentation PRs, please consider:

✅ Technical accuracy

• Code examples work as written
• Commands and configurations are correct
• Links resolve to the right destinations
• Prerequisites and requirements are accurate

✅ Clarity and completeness

• Instructions are clear and easy to follow
• Steps are in logical order
• Nothing important is missing
• Examples help illustrate the concepts

✅ User experience

• A new user could follow these docs successfully
• Common gotchas or edge cases are addressed
• Error messages or troubleshooting guidance is helpful

[mayankshouche]

lgtm! thanks for adding clarity here!