DOC-618: Enhance inline mode documentation: clarify CSS handling and …

[jeslynbo]

…styling recommendations

Ticket: DOC-618

Site: Staging branch

Changes:

• pages/use-tinymce-inline.adoc has a new section explaining CSS behavior in inline mode, including a code example showing the recommended approach
• partials/configuration/content_css.adoc NOTE is expanded to explain the risk and links to the inline mode page
• partials/configuration/content_style.adoc has a similar NOTE with cross-reference

Pre-checks:

• Branch prefixed with feature/<version>/, hotfix/<version>/, staging/<version>/, or release/<version>/.
• modules/ROOT/nav.adoc has been updated (if applicable).
• Included a release note entry for any New product features.
• If this is a minor release, updated productminorversion in antora.yml and added new supported versions entry in modules/ROOT/partials/misc/supported-versions.adoc.

Review:

• Documentation Team Lead has reviewed