[NikitkaRa]

First slice of SmartArt editing (after-beta pool in docs/gaps.md). Based on main; it doesn't depend on any open PR. #242 and #209 touch PowerPoint-read SmartArt, which this doesn't change.

Summary

• Model: Shape.diagram: Option<Diagram>, holding the layout kind and its nodes ({text, level}). It is skipped when None, so existing files are unchanged, and it is saved in .deckcraft.
• Engine: new crates/engine/src/cmd/smartart.rs.
  • Every edit regenerates the group's children inside its child rectangle, so the diagram keeps its place and size. Text typed straight into a diagram shape is read back into the nodes first.
  • New commands, each targeting the SmartArt group or any shape inside it:
    • smartArt.nodes (query)
    • smartArt.setNodes: the whole outline, tab-indented lines, or one node's text
    • smartArt.addNode: after, before, above or below, as in PowerPoint
    • smartArt.removeNode: sub-points move up a level
    • smartArt.promote and smartArt.demote: they move the node's whole subtree
    • smartArt.layout
• Layouts: sub-points become bullets inside their parent's shape in list, process, cycle, pyramid and matrix. Hierarchy is now a real tree: each subtree is as wide as its leaves, with connector lines.
• insert.smartArt: accepts tab-indented items or nodes, and returns {id}.
• UI:
  • A SmartArt Design contextual tab with Text Pane, Add Shape (After/Before/Above/Below), Promote, Demote and Layout.
  • A Text Pane task pane: Enter adds a line, Tab and Shift+Tab demote and promote, Backspace on an empty line removes it, and a line's edit is committed when it loses focus.
  • Inserting a SmartArt graphic opens the Text Pane.
• Docs: gaps.md (SmartArt entry rewritten), parity checklist (Text pane and layout switching M → P, recomputed), file-format and target-app parity.
• Not in this slice: PowerPoint-authored diagrams are still read as plain groups (no outline, so no Text Pane). The outline isn't written to .pptx dgm parts; the diagram saves as shapes, as before. There are six layouts.

Test plan

• Unit tests for the outline operations and the layout mapping (cmd::smartart::tests)
• Engine test: insert, type into a shape, add, demote, promote, remove, switch layout from a child, box unchanged, undo, .deckcraft round trip
• UI kittest: type in a Text Pane line, Enter adds a line, Tab demotes it
• Rendered hierarchy and list diagrams via deckcraft-cli render and checked them by eye
• cargo xtask ci (all 6 steps pass)

[echelon]

Thank you for this contribution, @NikitkaRa! It has landed on main and will ship in the next DeckCraft release.

If you haven't already, please come join us on Discord: https://discord.gg/artcraft