Adds File > Export > Current View as DXF: the visible bodies projected from the current camera onto 2D LINE/LWPOLYLINE entities, with hidden edges omitted or dashed.
Co-authored-by: cronos <19868002+crono2250@users.noreply.github.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Closes#1284. sheet.export_dxf writes layers by role (OUTLINE, CUT, TEXT or ETCH, dashed BEND_UP/BEND_DOWN, optional BEND_NOTES, POCKET_<side>_Z…_MM and PERFORATION), inner contours before the outline; text: cut|etch, bend_notes and note_height, per_body files. Letters are derived from the timeline, nothing new is saved (format unchanged). I merged main in (the export's parameter list keeps main's pocket layer names). Checked on main + this branch: cargo check --workspace, the engine cmd::sheet tests (160) and the io DXF tests.
sheet.export_dxf writes an AutoCAD 2000 drawing with ELLIPSE and SPLINE entities for ellipses, splines and text outlines instead of chords, with curves: arcs for machines that read only lines and arcs. Perforation circles go through the same writer. Closes#1089.
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