Add note on platform support for v7

Editor assessment

Documentation commit, correctly typed as 'docs' and safely excluded from version bumps and functional changelogs. The 'breaking' scope is a pragmatic way to signal the note concerns v7's breaking changes, though it is unconventional — scopes usually name components, so readers may initially misparse it. The subject 'add note on platform support for v7' is imperative and clear about the deliverable. As with most header-only messages, the substance is thin: which platforms are affected (deprecations, dropped browser versions) is left to the diff, and a sentence in the body would help anyone auditing release requirements without opening the change. Structure is valid; the PR reference '(#25823)' in the header doubles as traceability in lieu of a footer.