fix: vendor deps and fix CI go-version, timeout, GOTOOLCHAIN (HAN-414)

- Run go mod vendor to eliminate proxy.golang.org network dependency
- Set GOFLAGS=-mod=vendor at job env level so all go commands use vendor/
- Fix go-version from 1.23 to 1.24.0 to match go.mod
- Move GOTOOLCHAIN=local to job-level env (not per-step inline)
- Set cache: false on setup-go (cache is irrelevant with vendoring)
- Add timeout-minutes: 15 so failures are caught quickly instead of 3h

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: multica-agent <github@multica.ai>

vendor/github.com/miekg/dns/Makefile.release

@@ -0,0 +1,52 @@
+# Makefile for releasing.
+#
+# The release is controlled from version.go. The version found there is
+# used to tag the git repo, we're not building any artifacts so there is nothing
+# to upload to github.
+#
+# * Up the version in version.go
+# * Run: make -f Makefile.release release
+#   * will *commit* your change with 'Release $VERSION'
+#   * push to github
+#
+
+define GO
+//+build ignore
+
+package main
+
+import (
+	"fmt"
+
+	"github.com/miekg/dns"
+)
+
+func main() {
+	fmt.Println(dns.Version.String())
+}
+endef
+
+$(file > version_release.go,$(GO))
+VERSION:=$(shell go run version_release.go)
+TAG="v$(VERSION)"
+
+all:
+	@echo Use the \'release\' target to start a release $(VERSION)
+	rm -f version_release.go
+
+.PHONY: release
+release: commit push
+	@echo Released $(VERSION)
+	rm -f version_release.go
+
+.PHONY: commit
+commit:
+	@echo Committing release $(VERSION)
+	git commit -am"Release $(VERSION)"
+	git tag $(TAG)
+
+.PHONY: push
+push:
+	@echo Pushing release $(VERSION) to master
+	git push --tags
+	git push