feat: add command-line -LAYER support

[mlightcad]

Summary

• Add a new AutoCAD-style -LAYER command implementation in cad-simple-viewer with command-line-only interaction (no dialog dependency).
• Register and export the new command so it is available through the default command stack.
• Add English and Chinese i18n entries for command description, prompts, and keyword labels.
• Update README checklists (EN/ZH) to mark several implemented capabilities as completed.

Why

• Layer management in command-line workflows was missing in cad-simple-viewer.
• The project already supports keyword-driven, branching command patterns; -LAYER fills a core CAD command gap and aligns behavior with AutoCAD-style no-UI usage.

What Changed

• Added AcApLayerCmd with top-level branches:
  • ?, Make, Set, New, On, Off, Color, Freeze, Thaw, Lock, Unlock, Description.
• Implemented batch layer name parsing (*, comma-separated names), missing-layer reporting, and user notifications via event bus.
• Implemented explicit flag-bit updates for freeze/lock state changes to ensure thaw/unlock behavior is deterministic.
• Added layer listing output (console.table) plus command-line summary feedback.
• Wired command into registration:
  • import + registration under system command group as -layer.
  • export from command index.
• Added i18n content in:
  • packages/cad-simple-viewer/src/i18n/en/command.ts
  • packages/cad-simple-viewer/src/i18n/zh/command.ts
  • packages/cad-simple-viewer/src/i18n/en/jig.ts
  • packages/cad-simple-viewer/src/i18n/zh/jig.ts
• Added detailed TypeDoc comments across AcApLayerCmd type alias, class, and methods.
• Updated README progress checklist items in:
  • README.md
  • README.zh-CN.md

Risks / Notes

• -LAYER currently covers core branches but not full AutoCAD parity (e.g., additional subcommands like linetype/lineweight/plot/rename are not included yet).
• Layer listing is emitted to browser console (console.table), which is practical for dev/debug but may need refinement for production UX.
• README checklist updates are included in the same change set; reviewers may prefer separating documentation-only edits from command implementation.