fix(v2): pin onnxruntime_go to v1.12.1 to match onnxruntime 1.19.2 DLL

v1.31.0 requested ORT_API_VERSION 26 (onnxruntime 1.26); the field DLL is
Python 3.8's onnxruntime 1.19.2 (API 19), so GetApi(26) returned NULL and
init failed. v1.12.1 targets ORT API 19, matching the existing DLL with no
download. Verified: native cgo build of internal/spike compiles ort.go
against v1.12.1; Gio UI still cross-compiles for Windows.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

v2/go.mod

@@ -4,7 +4,7 @@ go 1.24.0
 
 require (
 	gioui.org v0.10.1
-	github.com/yalue/onnxruntime_go v1.31.0
+	github.com/yalue/onnxruntime_go v1.12.1
 	golang.org/x/image v0.26.0
 	golang.org/x/sys v0.39.0
 )

v2/go.sum

@@ -9,8 +9,8 @@ github.com/go-text/typesetting v0.3.4 h1:YYurUOtEb9kGSOz4uE3k4OpBGsp1dDL8+fjCeaF
 github.com/go-text/typesetting v0.3.4/go.mod h1:4qZCQphq4KSgGTAeI0uMEkVbROgfah8BuyF5LRYr7XY=
 github.com/go-text/typesetting-utils v0.0.0-20260223113751-2d88ac90dae3 h1:drBZzMgdYPbmyXqOto4YhhJGrFIQCX94FpR4MzTCsos=
 github.com/go-text/typesetting-utils v0.0.0-20260223113751-2d88ac90dae3/go.mod h1:3/62I4La/HBRX9TcTpBj4eipLiwzf+vhI+7whTc9V7o=
-github.com/yalue/onnxruntime_go v1.31.0 h1:1ln4YW1SFOFfGJZXe3jNOb2JUSt+l2pEneZfV8HdtFA=
-github.com/yalue/onnxruntime_go v1.31.0/go.mod h1:b4X26A8pekNb1ACJ58wAXgNKeUCGEAQ9dmACut9Sm/4=
+github.com/yalue/onnxruntime_go v1.12.1 h1:joCCmBnNjHy04jK9EMP/UV6oPPqySXlRgf3gcUcnI/g=
+github.com/yalue/onnxruntime_go v1.12.1/go.mod h1:b4X26A8pekNb1ACJ58wAXgNKeUCGEAQ9dmACut9Sm/4=
 golang.org/x/exp v0.0.0-20250408133849-7e4ce0ab07d0 h1:R84qjqJb5nVJMxqWYb3np9L5ZsaDtB+a39EqjV0JSUM=
 golang.org/x/exp v0.0.0-20250408133849-7e4ce0ab07d0/go.mod h1:S9Xr4PYopiDyqSyp5NjCrhFrqg6A5zA2E/iPHPhqnS8=
 golang.org/x/exp/shiny v0.0.0-20250408133849-7e4ce0ab07d0 h1:tMSqXTK+AQdW3LpCbfatHSRPHeW6+2WuxaVQuHftn80=