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>

.gitignore

@@ -0,0 +1,20 @@
+# dependencies / build
+node_modules/
+dist/
+*.log
+
+# large sample binaries (keep small Box/Duck/Cube samples for demos)
+samples/Br1.obj
+samples/Br1.mtl
+samples/GirderObjs/
+samples/Avocado.glb
+samples/ABeautifulGame.ktx2.glb
+samples/sample.obj
+public/samples/Avocado.glb
+public/samples/ABeautifulGame.ktx2.glb
+
+# diagnostic screenshots
+girder-smoke.png
+girder-zoom.png
+tex-test.png
+ply-test.png