Release 3.8.1.1: lighter idle UI poll, core cache, multicore ping.

Reduce idle CPU (cheap PollUI, binary cache, logbuf cap, DOM fingerprint),
speed ping/AWG HostPort, CopyBuffer pool; ship arm64 build and update notes.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/logbuf/buffer_test.go

@@ -0,0 +1,29 @@
+package logbuf
+
+import (
+	"strings"
+	"sync"
+	"testing"
+)
+
+func TestBufferConcurrentWriteAndCap(t *testing.T) {
+	b := New(64)
+	var wg sync.WaitGroup
+	for i := 0; i < 8; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < 40; j++ {
+				_, _ = b.Write([]byte("abcdefghij"))
+			}
+		}()
+	}
+	wg.Wait()
+	if b.Len() > 64+40 { // allow truncate marker overhead
+		t.Fatalf("len=%d exceeds soft cap", b.Len())
+	}
+	s := b.String()
+	if !strings.Contains(s, "abcdefghij") && !strings.Contains(s, "truncated") {
+		t.Fatalf("unexpected content %q", s)
+	}
+}