fix: hardcode onnxruntime to 1.24.2

[Davidnet]

Summary

• Roll back ONNX Runtime to 1.24.2 and pin onnxruntime_go to v1.27.0. The previous bump assumed multiple ONNX Runtime versions could be supported; in practice the C API headers in onnxruntime_go require a specific matching runtime version, so we're hardcoding a single version for now.
• Update docs/02-development-guide.md so all install/download/verify steps reference 1.24.2.

Follow-up

• A separate issue will be created to revisit the ONNX Runtime versioning strategy and establish a single source of truth (e.g. a build constant / Makefile variable) so the Go module version, the downloaded shared library, and the docs cannot drift apart again.

Test plan

• go build ./... succeeds with the pinned onnxruntime_go v1.27.0
• Backend starts locally with libonnxruntime.1.24.2.dylib / libonnxruntime.so
• Inference smoke test against the quantized model returns expected results

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[Copilot]

Pull request overview

Pins the project’s ONNX Runtime stack to a single compatible version by downgrading onnxruntime_go and updating development defaults/documentation to consistently use ONNX Runtime 1.24.2, reducing version drift and runtime/header mismatches.

Changes:

• Pin Go binding github.com/yalue/onnxruntime_go to v1.27.0.
• Switch local development default model variant to quantized.
• Update the development guide to install/download/copy ONNX Runtime 1.24.2.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/backend/config/config.development.json	Default local config now uses the quantized model variant.
go.mod	Pins onnxruntime_go to v1.27.0 to match the intended ORT C API compatibility.
go.sum	Adds checksums for onnxruntime_go v1.27.0 (but retains v1.28.0 sums).
docs/02-development-guide.md	Updates ONNX Runtime install/download instructions to 1.24.2.

Comments suppressed due to low confidence (1)

docs/02-development-guide.md:112

• On Linux, these steps copy the shared library to ./build/libonnxruntime.so, but the backend’s ONNX loader searches for versioned filenames like ./build/libonnxruntime.so.1.24.2 (or uses ONNXRUNTIME_SHARED_LIBRARY_PATH if set). As written, following the guide on Linux likely results in the library not being found at runtime. Update the instructions to either copy/symlink to build/libonnxruntime.so.1.24.2 (optionally also create build/libonnxruntime.so symlink) or document setting ONNXRUNTIME_SHARED_LIBRARY_PATH on Linux to the copied .so path.

cp "$LIB_PATH" ./build/libonnxruntime.1.24.2.dylib

# Find and copy library (Linux)
LIB_PATH=$(find .venv -name "libonnxruntime.so.*" | head -1)
cp "$LIB_PATH" ./build/libonnxruntime.so

</details>



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[Davidnet]

Follow-up issue for unifying the ONNX Runtime version: #407

[hanneshapke]

Also please sign the CLA.

[hanneshapke]

Please revert.

[Davidnet]

I have read the CLA Document and I hereby sign the CLA