[Header]: mark remaining community subcomponents as deprecated #965

Problem

The community Header is deprecated in favour of Header from @tedi-design-system/react/tedi, and so are HeaderLanguage and HeaderRole. Several other community Header subcomponents are not marked as deprecated.

Consumers get mixed signals and can keep building on these parts without any warning, even though the parent component is going away.

Solution

Mark the remaining subcomponents as deprecated in the same way as HeaderLanguage and HeaderRole, with these replacements from @tedi-design-system/react/tedi:

HeaderDropdown and HeaderModal don't get ExistsInTediReady. They are general-purpose building blocks, and there is no one-to-one TEDI-Ready version of them.

HeaderNotification is not publicly exported. It is only used through the community Header's notification prop. It gets the Storybook badge and a replacement note in its story description, but no @deprecated JSDoc.

• Add @deprecated JSDoc naming the replacement to each exported subcomponent above
• Set the Storybook status as listed above
• No runtime warnings: these subcomponents are meant to be used inside the community Header, which already warns (see the deprecation guide in .claude/skills/contributing/references/deprecation.md)
• No runtime or API changes (deprecation markers only)

SkipLinks is not part of this issue. There is no TEDI-Ready replacement yet, so it stays undeprecated until one exists.