Add illustrated GUI Tutorial (5 pages + 57 screenshots) Split the Alpha 2.4.1 end-to-end tutorial into a Tutorial hub plus four chapters (Accounts & Dashboard, Projects & Workspace, Build a Model, Simulate & Export). Merge imaging/segmentation + SUNDT glossary terms, add a Tutorial group to the sidebar, cross-link from Home and the GUI Walkthrough, and drop the stale FEATURES.md roadmap link.