Workbench task with geometry links

[trailcode]

Summary

• Sketch / Design / Workbench task toolbar. Workbench List stores geometry links (source_id) with their own placement, separate from Design bodies.
• Design cut, fuse, and common reuse the first operand's Shape_id, and cross-section clip keeps each survivor's id, so Workbench instances update instead of disappearing. Consumed operands still drop their links. Those booleans reject Workbench instances.
• Deleting a Design source still removes its Workbench links. Shape_remove_delta records the cascaded links, so undo restores them.
• .ezy mode slots 1, 3, and 24 stay Design Move / Rotate / Align shafts. Workbench Move / Rotate / Align shafts use new slots, so a file saved in the old Design tools does not open in Workbench.
• Align shafts axial sense, Workbench face pick / set frame, Extrude sketch face on the Sketch task, and the Workbench task icon.

Closes #268

Test plan

• EzyCad_tests --gtest_filter=Shp_test.Cut*:Shp_test.Fuse*:Shp_test.Common*:Shp_test.Undo_delete_design_restores_workbench_links:Shp_test.Design_geom_change_syncs_workbench_link:Shp_test.Workbench_json_round_trip_and_source_delete:Mode_helpers*
• Two Workbench instances of one solid: cut the Design body, both instances show the cut and keep their frames. Undo and redo.
• Delete the Design solid: its Workbench instances disappear. Undo restores the body and the instances.
• Cut on a Workbench selection is rejected; Design solids and instances stay.
• A project saved with mode integer 1, 3, or 24 opens in Design Move, Rotate, or Align shafts.
• Workbench Move / Rotate / Align shafts change instance pose only. Design Move does not move instances.
• Extrude sketch face is on the Sketch toolbar. Esc returns to Sketch inspection.

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Note

High Risk
Changes core document semantics (dual shape stores, boolean id reuse, mode enum/slots), persistence, and transform behavior across Design vs Workbench—regressions would affect saved projects and assembly-style workflows.

Overview
Introduces a Sketch / Design / Workbench task model: the toolbar has task switchers and only shows tools for the active task. Design still edits bodies in the Shape List (move/rotate/scale/align bake BREP); Workbench arranges linked instances in a new Workbench List pane (m_wbk_shps, persisted as .ezy workbench[] with sourceId + frame, no duplicate BREP).

Add to Workbench (button, context menu, or drag) creates placements that track Design geometry when the same Shape_id survives edits. Cut, fuse, common, and cross-section clip now reuse the first/survivor operand id where appropriate; Shape_replace_delta avoids dropping links when the same id is re-inserted. Workbench Move / Rotate / Align shafts update instance pose only; G/R/J follow the current task; S stays Design Scale. Idle modes rename to Design_inspection / Sketch_inspection (legacy names still parse).

Also ships Workbench toolbar/list polish (face pick, set frame, task sync on list selection), align-shafts default axial sense, extrude on the Sketch task, changelog fixes (transform mid-drag, sketch overlaps, wasm link), docs/agent plans, and the Workbench task icon.

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