Extrude/transform preview performance and multi-select retention

[trailcode]

Summary

• Extrude: hybrid live preview (shaded prism for simple faces; translated face copies for dense faces when Settings Extrude fast preview is on); both-sides lite faces; finalize always builds the solid.
• Move / Rotate / Scale: preview without per-frame Redisplay; disable dynamic highlight while active to avoid ghost wireframes; keep and restore multi-selection on enter, finalize, and Escape; skip AIS select on the finalize LMB release; undo/redo returns to Normal instead of re-entering the free-drag tool.
• Scripting: ezy.view.set_selected(...) for Python, Lua, and the remote client.

Closes #225

Test plan

• Desktop Debug/Release build; ctest -C Release
• Extrude dense face with Extrude fast preview on/off; both-sides; finalize solid
• Move/Rotate/Scale complex solid: smooth drag, no ghost at original pose
• Select two solids → G → move → LMB finalize: both stay selected; Escape cancel same
• Undo after multi move: Normal mode, no auto-drag of one shape
• Script: view.set_selected(view.get_selected())
• Spot-check Settings Extrude fast preview, docs/usage.md / usage-settings.md / scripting.md, CHANGELOG

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Note

Medium Risk
Touches core viewer input (mode enter, LMB routing, undo mode restore) and transform/extrude preview paths; behavior changes are user-visible but localized to interactive tools rather than persistence or auth.

Overview
Improves sketch-face extrude and Move / Rotate / Scale responsiveness, and fixes selection loss around transform and extrude workflows.

Extrude adds a hybrid drag preview: simple faces still get a shaded MakePrism solid; dense faces (when Settings → Sketch → Appearance → Extrude fast preview is on, default edge threshold 24) preview by translating face copies, including both ends when Both sides is on. Finalize always builds the real solid; length dimension handling is reworked for both-sides toggles.

Move / Rotate / Scale stop per-frame Redisplay during preview—only SetLocalTransformation plus a viewer redraw—and turn off AIS dynamic highlight while those tools are active to avoid wireframe ghosts on stale selection BVHs. Entering a transform mode snapshots and restores multi-selection via set_selected_shps and seeds operands with begin(); finalize/cancel re-selects all operands and skips AIS press/release on the finalize LMB so release cannot collapse multi-select. Undo/redo maps stored Move/Rotate/Scale back to Normal instead of re-entering free-drag.

Scripting: ezy.view.set_selected(...) (Python, Lua, remote ezycad client). Settings persist gui.extrude_fast_preview and gui.extrude_fast_preview_edge_threshold.

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