ci: tighten GitHub Actions migration

[adlio]

Summary

• add an explicit build job so GitHub Actions matches the old CircleCI build/test split more closely
• switch workflows to use the Go version from go.mod, add concurrency controls, and keep release creation idempotent
• remove the obsolete .travis.yml file and fix the release tag trigger glob

Test Plan

• go test ./...
• go test -race -coverprofile=coverage.out -covermode=atomic ./...
• /tmp/golangci-bin/golangci-lint run ./...
• /tmp/actionlint-bin/actionlint