feat: multi-format 3D viewer with large-file OBJ streaming, Z-up, projection/outline UI

Three.js viewer supporting glb/gltf/obj/fbx/dae/ifc/ply via both server (SSR)
and drag&drop (CSR) paths.

- Streaming OBJ parser (src/viewer/objStream.ts) for files past the V8 max
  string length (>~1GB text) that OBJLoader can't handle; indexed geometry,
  per-vertex color from MTL Kd, float64 recenter baked in.
- In-viewer float64 recenter (objRecenter.ts) for huge CAD/survey coordinates
  (~1e8) so float32 vertex buffers keep precision (no cracked faces).
- Z-up right-handed world; Y-up formats rotated on load.
- OBJ+MTL+texture drag&drop (LoadingManager URL-modifier maps dropped images).
- OrbitControls ground-plane panning (road/rail alignment workflow).
- UI: Zoom Fit, perspective/orthographic toggle, feature-edge outline.
- DoubleSide for CAD OBJ; PLY mesh + point-cloud support.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tools/copy-decoders.mjs

@@ -0,0 +1,46 @@
+// Copies Draco + KTX2/Basis decoder WASM from three.js into public/ so the
+// runtime paths /draco/ and /basis/ resolve (version-matched to installed three).
+// Also copies the web-ifc single-thread WASM to public/web-ifc/ for the IFC path.
+// Runs automatically via `npm install` (postinstall). Safe to re-run.
+import { cpSync, copyFileSync, existsSync, mkdirSync } from 'node:fs';
+import { dirname, resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const root = resolve(__dirname, '..');
+
+const libs = resolve(root, 'node_modules/three/examples/jsm/libs');
+const targets = [
+  [resolve(libs, 'draco/gltf'), resolve(root, 'public/draco')],
+  [resolve(libs, 'basis'), resolve(root, 'public/basis')],
+];
+
+if (!existsSync(libs)) {
+  console.warn('[copy-decoders] three not installed yet — skipping (will run on next install).');
+  process.exit(0);
+}
+
+for (const [src, dest] of targets) {
+  if (!existsSync(src)) {
+    console.warn(`[copy-decoders] source missing: ${src}`);
+    continue;
+  }
+  mkdirSync(dest, { recursive: true });
+  cpSync(src, dest, { recursive: true });
+  console.log(`[copy-decoders] ${src} -> ${dest}`);
+}
+
+// web-ifc single-thread WASM (+ MT build if present) for the IFC load path.
+const ifcSrcDir = resolve(root, 'node_modules/web-ifc');
+const ifcDest = resolve(root, 'public/web-ifc');
+if (existsSync(ifcSrcDir)) {
+  mkdirSync(ifcDest, { recursive: true });
+  for (const wasm of ['web-ifc.wasm', 'web-ifc-mt.wasm']) {
+    const src = resolve(ifcSrcDir, wasm);
+    if (!existsSync(src)) continue;
+    copyFileSync(src, resolve(ifcDest, wasm));
+    console.log(`[copy-decoders] ${src} -> ${resolve(ifcDest, wasm)}`);
+  }
+} else {
+  console.warn('[copy-decoders] web-ifc not installed yet — skipping IFC wasm.');
+}