[reorg fix] [DAL-834] Document OAuth scope restrictions

[jhgilbert]

🤖 Auto-generated fix for #38520.

@imaique — the docs repo reorg created merge conflicts in your PR #38520. This is an auto-generated replacement with the file paths fixed; please use it instead of the original.

This PR replays the commits from #38520 with file paths translated to the post-reorg hugo/ layout. The original commits are preserved — same messages and authorship.

The original PR (#38520) will be closed in favor of this one.

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• Ready for merge

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Original PR description:

What does this PR do? What is the motivation?

Fixes DAL-834

Updates the Mobile and Third-Party Access documentation to:

• Describe how Application Scope Management handles future scopes.
• Clarify support for the Datadog Mobile App and MCP applications.
• Document required Mobile scopes and authorization revocation behavior.

Merge readiness

• Ready for merge

AI assistance

Used Codex for source research, initial drafting, and style checks. The final wording was validated against shipped behavior.

Additional notes

Validation:

• git diff --check passed.
• Added-content checks found no em dashes, restricted style terms, or internal references.
• Vale was not run locally because the binary is not installed in this environment.

[datadog-prod-us1-4]

⚠️ Warnings

🚦 2 Pipeline jobs failed

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See error

FileNotFoundError: No such file or directory: 'local/bin/py/preview-links-template.mako'

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[imaique]

Superseded by #39469, which includes this documentation and removes the outdated MCP-only availability limit.