feat: scaffold Go module with version command, Makefile and goreleaser config

internal/version/version.go

@@ -0,0 +1,7 @@
+// Package version carries the build-time version of the agent-lib binary.
+package version
+
+// Version is injected at build time via
+// -ldflags "-X internal/version.Version=<version>". It defaults to "dev"
+// for plain `go build` runs.
+var Version = "dev"