v1.6.0

Arte Ogre 1.6.0 — selection outlines for every selection tool

Fixes a bug where the marching-ants selection outline was never drawn for mask-based selections, making those tools look dead even though the selection was actually created. Affected tools: Magic Wand, Select by Color, Quick Selection, Ellipse Select, and all three lassos (Polygon, Freehand, Magnetic). Rectangle Select was unaffected.

• Root cause: mask selection boundaries are emitted as 1-pixel unit edge segments, and egui's line-segment pixel rounding collapses any axis-aligned 1-px segment to zero length — every one of those segments rendered as nothing. Rect selections survived because they emit four long edges.
• Fix: the boundary unit edges are now chained into closed polylines (cached once per selection change), the black base is stroked as a single path per loop, and the white marching dashes are walked along the loop's arc length, which also makes dashes continuous around corners.
• Verification: regression tests tessellate the outline through egui's real rounding path and assert visible geometry; every affected tool was re-verified live end-to-end.