Improve split-post workflow for multi-platform releases

Enhance the split-post functionality in the Roadmap to better support teams releasing features across multiple platforms (e.g., Web + Mobile) with different release timelines.

Requested Improvements:

Automatic Duplication of Post Details

  1. When splitting a roadmap item, all content and metadata (title, description, fields, custom fields) should be copied into the new posts automatically to avoid manual re-entry.

Platform Selection During Split

  1. Show the Platform field directly on the split-post screen so Web/Mobile can be assigned immediately, rather than opening each post afterwards.

Auto-Link Split Posts

  1. Posts created through a split should automatically reference each other via the Related posts relation to maintain context.

Full Metadata Availability

  1. Ensure all metadata fields are editable at creation time, not only after a post exists, so users can configure everything in one step.

Goal:

Make split-post handling on the Roadmap smoother, reduce the risk of missing platform-specific work, and support cleaner release management across Web and Mobile.