feat: opt into LibreDWG DWG parsing and upgrade to v1.6.0

[mlightcad]

Summary

• Upgrade @mlightcad/cad-simple-viewer stack to 1.6.0 / data-model 1.13.0, and rename applyUiTheme → acedApplyUiTheme.
• Make DWG support an explicit GPL opt-in: depend on @mlightcad/libredwg-converter, register via src/registerLibreDwg.ts before createInstance, and copy LibreDWG worker + wasm into dist/assets/.
• Bump vite-plugin-static-copy to v4 (rename: { stripBase: true }) and document the new worker/wasm deployment pattern in README.

Test plan

• pnpm install && pnpm build — confirm 4 static assets copied (mtext worker, libredwg worker, wasm, viewer-runtime)
• pnpm dev — open DXF on both index.html and no-plugin.html
• Open a DWG and confirm LibreDWG worker + wasm load (no missing .wasm errors)
• With-plugins page: toolbar / Layer Manager / export still work
• Spot-check README snippets against vite.config.ts and registerLibreDwg.ts

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