Remaining issues: * [x] Remove the deprecated add/removeContent API (after ensuring all remaining consumers are ported) * [x] Make Content::parent and Content::topLevel const-correct (needs removal of the MessageCore::NodeHelper iteration methods) * [x] Make Content::decodedText const (needs the move of the decoded flag from Headers::CTE to ContentPrivate, and for that potentially new API to indicate whether you set a decoded or encoded content on a KMime::Content node) * [x] DateFormatter probably should move out to its single use, which would remove the dependency on translations even. * [x] Remove or change Content::defaultCharset(), that doesn't return UTF-8 yet... * [ ] Replace Header::from7Bit overloads with a single one taking a QByteArrayView * [x] Move to automatically generated forwarding includes. * [x] Fix Windows unit test and require passing unit tests on all platforms. * [ ] Use unique_ptr for memory management * [ ] Replace bool parameters with enums * [ ] Port API documentation to qdoc * [ ] Adjust to KF naming and versioning (in a branch?) and go through the KF review process * [ ] Timing: aim for KF 6.23 (February 2026) and for KDE Gear 26.04