Sketch dimension inspector controls and arrow-size setting

[trailcode]

Sketch List: per-dimension controls (visibility + offset) and dimension arrow-size setting

Summary

Improve sketch dimension usability by exposing per-dimension controls in Sketch List and adding a global arrow-size setting for dimension visuals.

What was added

• Sketch List inspector now supports expandable sketch details with a Dimensions section.
• Each dimension row includes:
  • visibility checkbox
  • numeric offset input for label flyout distance from edge (0 keeps automatic behavior)
• Dimension rows are column-aligned (show, label, offset) for better readability in narrow panes.
• New Settings control under Settings -> Sketch:
  • Dimension arrow size
  • applies to sketch dimensions and extrude preview dimensions
  • persisted in settings JSON as gui.edge_dim_arrow_size

Persistence / compatibility

• Sketch JSON length_dimensions supports:
  • legacy: [node_lo, node_hi]
  • with visibility: [node_lo, node_hi, visible]
  • with visibility + custom offset: [node_lo, node_hi, visible, flyout_offset]
• Loader remains backward compatible with older documents.

Why this matters

• Faster control of drawing clarity directly in Sketch List.
• Better handling of dense sketches where some dimensions should be hidden.
• Fine-grained adjustment of dimension label distance without leaving context.
• Better visual consistency by allowing arrow-size tuning in Settings.

Acceptance criteria

• In Sketch List, expanding a sketch shows Dimensions, Edges, and Faces.
• Each dimension row has an independent visibility checkbox.
• Each dimension row has an editable offset double input.
• Setting offset to 0 falls back to automatic flyout behavior.
• Per-dimension visibility and offset survive save/load.
• Settings -> Sketch -> Dimension arrow size updates existing dimensions immediately.
• Arrow-size setting persists across app restarts.

Notes

• Offset control uses OCCT dimension flyout magnitude while preserving the orientation sign chosen by existing outside/inside logic.

[trailcode]

Done