feat(ui): rebuild the viewer UI with HMDesign components

New React UI around the unchanged engine (#1). GNB_ONLY page:

- AppHeader: GNB + GNBBrand; sample drawings in GNBNav (NavigationMenu)
  and GNBMobileMenu (same data, real ?model= links); file open and
  about/notice in GNBUtilities.
- DwgViewerCanvas: useRef/useEffect wrapper. new Viewer2D(host) on
  mount, option props diffed and pushed through the engine setters,
  onSelect/onPointerWorld/onViewChange forwarded to React. Viewer2D has
  no dispose(), so teardown stops the rAF loop / WebGL context from
  outside (also needed for StrictMode double mount).
- ViewerToolbar: Model/Layout ToggleGroup (sample's visibility rule),
  Fit, 2.5D and canvas-theme Toggles, window Toggles.
- FloatingPanel: HM Card in a fixed frame; drag/collapse via the ported
  makePanelDraggableAndCollapsible, CSS resize.
- LayersPanel (FilterBar search, Switch per layer, show/hide all via
  LayerPanelManager), PropertiesPanel (formatEntityProperties → Badge +
  Table, zoom to selection), OptionsPanel (Switch/Slider/Input, IndexedDB
  through optionsStore, reset).
- Load feedback per HMDesign: Progress for the measurable part
  (download bytes, stage steps) and LoadingScreen for the blocking
  WASM parse / Viewer2D.load(), painted before each blocking stage.
- StatusBar with status line, zoom %, live CAD coordinates in the
  bottom-right corner; AboutDialog keeps the acadrust MPL-2.0 notice,
  THIRD-PARTY-NOTICES and the local patch reachable.
- Drag & drop, ?model= auto-load, F shortcut, ResizeObserver resync.

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

src/main.tsx

@@ -0,0 +1,16 @@
+import { StrictMode } from "react"
+import { createRoot } from "react-dom/client"
+import "./index.css"
+import "./hm-theme.css"
+import { setDefaultFontUrl } from "./engine/viewer2d/slugText"
+import { App } from "./App"
+
+// Host static asset for TEXT/MTEXT glyphs (Hangul + Latin). Must be set before the first Viewer2D is
+// constructed: its constructor warms SlugTextEngine with this URL.
+setDefaultFontUrl(`${import.meta.env.BASE_URL}fonts/NanumGothic-Regular.ttf`)
+
+createRoot(document.getElementById("root")!).render(
+  <StrictMode>
+    <App />
+  </StrictMode>,
+)