feat: implement agent-notify CLI with hooks and tmux passthrough

Add OSC 777 notification sender, Cursor/Claude hook adapters,
config/install commands, and README for Ghostty + tmux setup.

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

internal/notify/send_test.go

@@ -0,0 +1,42 @@
+package notify
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestSendDirect(t *testing.T) {
+	var buf bytes.Buffer
+	err := Send(SendOptions{
+		Protocol: "osc777",
+		Title:    "Cursor — app",
+		Body:     "等待输入",
+		Writer:   &buf,
+		InTmux:   false,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Contains(buf.Bytes(), []byte("777;notify")) {
+		t.Fatalf("missing osc777: %q", buf.String())
+	}
+}
+
+func TestSendTmuxUsesPassthroughWhenNoTTY(t *testing.T) {
+	var buf bytes.Buffer
+	err := Send(SendOptions{
+		Protocol:  "osc777",
+		Title:     "t",
+		Body:      "b",
+		Writer:    &buf,
+		InTmux:    true,
+		Layers:    1,
+		ClientTTY: "",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.HasPrefix(buf.Bytes(), []byte("\033Ptmux;")) {
+		t.Fatalf("expected passthrough prefix, got %q", buf.String())
+	}
+}