feat: add AutoCAD-style layer commands and reorganize command modules

[mlightcad]

Summary

This PR expands layer-management capabilities in the CAD viewer and refactors the command structure to make the codebase easier to navigate and extend.

What Changed

• added AutoCAD-style layer commands, including -LAYER, LAYDEL, LAYFRZ, LAYOFF, and LAYERCLOSE
• registered the new layer commands in AcApDocManager
• wired LAYERCLOSE to the viewer through the shared event bus so it closes the layer manager only when that palette tab is active
• reorganized command implementations into feature-based folders:
  • convert
  • draw
  • layer
  • measure
  • modify
  • review
• simplified command exports and updated imports accordingly
• added and updated English and Chinese command text for the new layer-related workflows
• added layer-related SVG assets and exports in cad-viewer, including icons for layer state, color, line style, and line weight
• added unit coverage for AcApLayerCloseCmd

Why

• improve parity with familiar AutoCAD layer workflows
• make command implementations easier to maintain by grouping them by domain
• prepare the viewer UI and command system for richer layer operations and palette interactions

Notes

• LAYOFF and LAYFRZ keep AutoCAD-style settings and undo flows, while viewport-specific behavior falls back to the current viewer capabilities where needed
• LAYERCLOSE is intentionally scoped to close the layer manager only when the layer tab is currently open

Testing

• added AcApLayerCloseCmd unit test