go get bumped go.mod to 'go 1.25.0' (modernc requirement), but CI used setup-go
1.24 and the image used golang:1.24 — with GOTOOLCHAIN=local the test step failed
('requires go >= 1.25.0'). Install the exact version from go.mod via
go-version-file, bump the builder image to golang:1.25-alpine, and drop the stray
GOTOOLCHAIN override in build.ps1.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>