Phase 5: scaffold Crucible (sow-tools) — dispatcher + builder shims, container, PR-first CI, fail-closed (D11, D19).

cmd/crucible/main.go

@@ -0,0 +1,10 @@
+// Command crucible is the Crucible dispatcher: `crucible <builder> [args]`.
+package main
+
+import (
+	"os"
+
+	"gitea.westgate.pw/ShadowsOverWestgate/sow-tools/internal/dispatch"
+)
+
+func main() { os.Exit(dispatch.Main(os.Args[1:])) }