Add bone sketch tool; extrude Both sides default; wasm CMake/link fixes

[trailcode]

Summary

Add a Bone sketch creation tool (connecting-rod outline), default Extrude Both sides on, and fix Emscripten configure/link on modern emsdk.

Goals

• Add bone (Shift+U / mode.add_bone): place two centers, radius 1, radius 2, waist; optional holes and permanent Bone A / Bone B nodes; commit exits to Sketch inspection
• Options: Add center nodes (default on), Holes (None / One radius / Two radii); persist gui.bone_add_center_nodes / gui.bone_holes
• User docs + hotkeys + icon (Sketcher_CreateBone)
• Extrude Options Both sides defaults to on (session sticky)
• Wasm: detect Emscripten via EMSCRIPTEN / CMAKE_SYSTEM_NAME; link FreeType from OCCT wasm install

Notes

Waist is minimum neck thickness (offset toward smaller end when radii differ). Waist cutters are tangent to both end circles.