[material_ui, cupertino_ui] Migrate dartpad TODOs to <callout-box>

[dkwingsmt]

Background

Dartdoc 9.0.7 added support for <callout-box> (what we used to call the blue container).

What's changed

This PR migrates all should-be Dartpad instances in API docs to <callout-box>. This is what it looks like:

This PR also disables unintended_html_in_doc_comment because <callout-box> is not recognized by the linter for now. An issue has been filed: dart-lang/sdk#63777

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style, or I have commented below to indicate which documented exception this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

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Footnotes

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[dkwingsmt]

/gemini review

[gemini-code-assist]

Code Review

This pull request wraps example documentation blocks in tags across multiple Cupertino and Material UI components, and disables the unintended_html_in_doc_comment linter rule. Feedback on the changes highlights that placing regular // TODO comments inside contiguous /// doc comment blocks terminates the block, causing dartdoc to ignore the preceding documentation. The reviewer suggests moving these // TODO comments outside of the doc comment blocks to ensure correct API documentation generation.

[dkwingsmt]

FYI this PR is now ready for review.