Improve portable launch, forge persistence, and operator auth UX.

Persist build extra_files for Build Manager history, print dashboard login on every start, add libp2p for Mesh P2P forge, defer WebSocket until login, and split devrun.bat from LAUNCH.bat with USB deck auto-detection.

agent/deploy/common_test.go

@@ -1,6 +1,7 @@
 package deploy
 
 import (
+	"os"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -118,3 +119,18 @@ func TestResolveInstallDirWithFallback(t *testing.T) {
 		t.Fatal("empty dir")
 	}
 }
+
+func TestWantsSpreadInstall(t *testing.T) {
+	orig := os.Args
+	t.Cleanup(func() { os.Args = orig })
+
+	os.Args = []string{"agent"}
+	if WantsSpreadInstall() {
+		t.Fatal("expected false without flag")
+	}
+
+	os.Args = []string{"agent", "--spread-install"}
+	if !WantsSpreadInstall() {
+		t.Fatal("expected true with --spread-install")
+	}
+}