feat: React19+HMDesign shell with ported DWG/DXF viewer engine

Scaffolds the new app (Vite+React19+Tailwind v4) on HMDesign via git
submodule + npm workspace, ports src/viewer2d/* and optionsStore.ts
unchanged, and rebuilds the vanilla UI (toolbar/layers/properties/
options panels, coord readout, license dialog, load progress) as HM
Design System components. Panel drag/collapse ported from
panelUtils.ts as a React hook; Measure UI intentionally left
unwired per original app parity.

Typecheck and dev-server module serving verified; in-browser
rendering not yet verified in this session (no browser tool
available) — needs manual check.

Refs #1

vite.config.ts

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vite';
+import react from '@vitejs/plugin-react';
+import tailwindcss from '@tailwindcss/vite';
+
+export default defineConfig({
+  plugins: [react(), tailwindcss()],
+  server: { port: 5173, strictPort: true },
+  // HMDesign (git submodule) has its own example/export HTML entries with their
+  // own `@/...` path aliases — without pinning `entries`, Vite's dependency
+  // scanner crawls every *.html under the project root and trips over them.
+  optimizeDeps: { include: ['three', 'dxf-parser', 'opentype.js'], entries: ['index.html'] },
+  assetsInclude: ['**/*.wasm'],
+});