Client-side stereo detection transfer via ONNX (first pass)

[mattdawkins]

First pass at warping a detection from one camera to the other entirely
client-side (web + Electron renderer), with no backend, by running VIAME's
epipolar template-matching stereo model (stereo measurement "method 1")
exported to ONNX and executed with onnxruntime-web.

This is the client counterpart to the desktop backend stereo service: the
desktop ViewerLoader warps via native IPC (stereoTransferLine /
stereoTransferPoints); this does the equivalent correspondence search in the
browser so it also works on the web.

What's here (client/dive-common/use/stereo/)

• StereoOnnxMatcher — loads the match ONNX model and warps source points to
  target points (epipolar candidate generation + NCC along the curve).
• calibration.ts / npz.ts — parse .npz/.json calibration in-browser
  (mirrors read_stereo_rig), plus invertRig to swap source/target camera.
• image.ts — RGBA to BT.601 grayscale (matches OpenCV BGR2GRAY used by the NCC).
• frameSource.ts — read full-res frame pixels from a GeoJS viewer.
• useStereoOnnxTransfer — on stereo-annotation-complete, warp a box (corners)
  or head/tail line (keypoints) to the other camera and write the feature.
• Web glue: platform/web-girder/useStereoOnnxWeb.ts, bound to the Viewer's
  stereo-annotation-complete event in the web ViewerLoader.vue.

onnxruntime-web is added as a dependency. The exported model is served as a
static asset (default /models/stereo_match.onnx).

Testing

• Core is unit-tested (__tests__/stereoOnnx.spec.ts, runs under npm test):
  calibration parsing, grayscale, and point warping validated against the VIAME
  C++/Python reference (matches to ~0.25 px) via onnxruntime-web in Node.
• The web glue (frame-pixel read, ViewerLoader binding, calibration retrieval) is
  type-checked and lint-clean but has not been live-tested in a running web
  viewer with a real stereo dataset.

Notes

• Disparity search range is currently a permissive default; should become a user
  setting.
• DINO-augmented method 2 exists on the VIAME side but is not wired here yet.