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

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "HMDesign"]
+	path = HMDesign
+	url = https://gitea.hmac.kr/b25027/HMDesign.git