Add the parametric sketch workspace with multi-source tool bins

[jaak0b]

Summary

A parametric 2D sketch workspace so tool outlines can be drawn instead of photographed, integrated into the existing tool bin pipeline, plus the data-model rework it motivated.

• Sketch editor on the PlaneGCS constraint solver (WASM, LGPL notice in the README, wasm ships as a separate asset): lines, arcs, tangent arcs, circles, rectangles, slots, mirror lines, construction geometry, undo/redo, CAD constraint glyphs.
• Fusion-style dimensions: place-at-label flow with witness lines and angle arcs, length/distance/point-line/radius/diameter/angle kinds, horizontal/vertical/aligned flavors, angle quadrant picking, driven (reference) dimensions with an over-constrain keep-as-reference offer.
• Region extraction: planar arrangement (analytic intersections, DCEL face traversal) shades every enclosed area for picking, so overlapping geometry (a line across a circle) yields usable outlines.
• Multi-part tools: several picked regions become one rigid tool (alignment-pin patterns keep their constrained spacing); overlapping pockets across tools now merge with a non-blocking warning.
• Multi-source bins: per-tool origin (photo trace, sketch, primitive), trace sessions per photo sheet, several sheets plus sketches in one bin, source-card list stage; plan file v11 with v10/legacy migrations.
• Fusion-canvas reference photos: multiple images, manipulator handles, two-click calibrate (pure uniform scale), per-image opacity.

Verification

• 1417 unit tests and the production build green (CI runs the same).
• Every task and each feature wave passed an independent review pass; all findings fixed and re-reviewed.
• Owner checks still owed before merge: browser pass over the new UI and an Orca Slicer check of an exported multi-part bin.

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