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/stats/cpu_windows_test.go

@@ -0,0 +1,35 @@
+//go:build windows
+
+package stats
+
+import "testing"
+
+func TestFiletimeToUint64(t *testing.T) {
+	ft := filetime{LowDateTime: 0xDEADBEEF, HighDateTime: 0x00001234}
+	want := (uint64(0x1234) << 32) | 0xDEADBEEF
+	if got := filetimeToUint64(ft); got != want {
+		t.Fatalf("got %x want %x", got, want)
+	}
+	if filetimeToUint64(filetime{}) != 0 {
+		t.Fatal("zero filetime should be 0")
+	}
+}
+
+func TestCPUBusyPercentFromDeltas(t *testing.T) {
+	tests := []struct {
+		idle, total float64
+		want        float64
+	}{
+		{idle: 25, total: 100, want: 75},
+		{idle: 0, total: 100, want: 100},
+		{idle: 100, total: 100, want: 0},
+		{idle: 0, total: 0, want: 0},
+		{idle: -10, total: 50, want: 100}, // over 100% busy clamped
+		{idle: 200, total: 100, want: 0}, // negative busy clamped to 0
+	}
+	for _, tc := range tests {
+		if got := cpuBusyPercentFromDeltas(tc.idle, tc.total); got != tc.want {
+			t.Fatalf("idle=%v total=%v: got %v want %v", tc.idle, tc.total, got, tc.want)
+		}
+	}
+}