feat(engine): port the viewer engine and panel logic unchanged

Copy the vanilla engine from dwg-dxf-viewer-sample verbatim (#1):

- src/engine/viewer2d/* (Viewer2D.js incl. the 2.5D view, parsers,
  acadrust-dwg WASM, cadSpaces, slugText, linParser/linData,
  fixDwgKoreanText, ...)
- src/engine/{layerPanel,panelUtils,propertyInspector,optionsStore}.ts

The relative layout is kept (engine/viewer2d next to the panel files),
so not even import paths changed; `diff -r --strip-trailing-cr` against
the sample is empty. public/ (NanumGothic, samples, licenses, module
map) is copied as is.

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

src/engine/viewer2d/acadrust-dwg/acadrust_dwg.d.ts

@@ -0,0 +1,53 @@
+/* tslint:disable */
+/* eslint-disable */
+
+export function parse_dwg(bytes: Uint8Array): any;
+
+/**
+ * The same parseResult as [`parse_dwg`], returned as a JSON string for the
+ * caller to hand to `JSON.parse`. Prefer this on anything but small drawings.
+ *
+ * Materializing the whole result as a `serde_json::Value` is what makes big
+ * files unopenable. The tree costs ~150× the DWG on the heap (a 19 MB drawing
+ * peaks near 2 GB), and the wasm allocator's per-allocation cost rises with the
+ * live heap, so conversion goes quadratic — measured 352 s in wasm for work
+ * that takes 2.5 s natively. Converting one entity at a time and appending its
+ * JSON text keeps the live heap flat and the cost linear.
+ */
+export function parse_dwg_json(bytes: Uint8Array): string;
+
+export type InitInput = RequestInfo | URL | Response | BufferSource | WebAssembly.Module;
+
+export interface InitOutput {
+    readonly memory: WebAssembly.Memory;
+    readonly parse_dwg: (a: number, b: number) => [number, number, number];
+    readonly parse_dwg_json: (a: number, b: number) => [number, number, number, number];
+    readonly __wbindgen_malloc: (a: number, b: number) => number;
+    readonly __wbindgen_realloc: (a: number, b: number, c: number, d: number) => number;
+    readonly __wbindgen_externrefs: WebAssembly.Table;
+    readonly __externref_table_dealloc: (a: number) => void;
+    readonly __wbindgen_free: (a: number, b: number, c: number) => void;
+    readonly __wbindgen_start: () => void;
+}
+
+export type SyncInitInput = BufferSource | WebAssembly.Module;
+
+/**
+ * Instantiates the given `module`, which can either be bytes or
+ * a precompiled `WebAssembly.Module`.
+ *
+ * @param {{ module: SyncInitInput }} module - Passing `SyncInitInput` directly is deprecated.
+ *
+ * @returns {InitOutput}
+ */
+export function initSync(module: { module: SyncInitInput } | SyncInitInput): InitOutput;
+
+/**
+ * If `module_or_path` is {RequestInfo} or {URL}, makes a request and
+ * for everything else, calls `WebAssembly.instantiate` directly.
+ *
+ * @param {{ module_or_path: InitInput | Promise<InitInput> }} module_or_path - Passing `InitInput` directly is deprecated.
+ *
+ * @returns {Promise<InitOutput>}
+ */
+export default function __wbg_init (module_or_path?: { module_or_path: InitInput | Promise<InitInput> } | InitInput | Promise<InitInput>): Promise<InitOutput>;