chore: scaffold Vite + React 19 + Tailwind v4 app on HMDesign

Start the React rebuild of the DWG/DXF viewer (#1).

- HMDesign is a git submodule (vendor/HMDesign, main) and its
  packages/ui is an npm workspace, so @hm-design/ui resolves to the
  submodule and shares this repo's node_modules.
- scripts/setup-hmdesign.mjs (postinstall) builds the package dist and
  points vendor/HMDesign/node_modules at ours with a junction, because
  HMDesign's build script reads typescript/shadcn from its own root.
  Nothing inside the submodule is modified.
- Versions follow HMDesign (react 19.3.0, vite 8.3.0, tailwindcss
  4.3.3, typescript 7.0.2) and the sample (three 0.185.1, dxf-parser
  1.1.2, opentype.js 2.0.0).
- CSS entry: tailwindcss + @hm-design/ui/tailwind.css (index.css).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "vendor/HMDesign"]
+	path = vendor/HMDesign
+	url = https://gitea.hmac.kr/b25027/HMDesign.git
+	branch = main