actions/setup-go@v5 was failing silently (0s steps) likely due to
network issues downloading Go from GitHub. Install Go directly from
go.dev which is more accessible.
Also remove Docker job (not needed yet) and simplify to 3 jobs.
The curl-based install script downloads from raw.githubusercontent.com
which is unreliable in some network environments. go install is more
reliable and uses the Go module proxy.
Mirror of .github/workflows/ci.yml adapted for Gitea Actions:
- Replace golangci-lint-action with direct install script
- Remove upload-artifact (not needed on Gitea)
- Same 4-job structure: lint → test → build → docker
