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/osc_test.go

@@ -0,0 +1,26 @@
+package notify
+
+import "testing"
+
+func TestBuildOSC777(t *testing.T) {
+	seq := BuildSequence("osc777", "Claude — proj", "等待输入")
+	want := "\033]777;notify;Claude — proj;等待输入\007"
+	if seq != want {
+		t.Fatalf("got %q want %q", seq, want)
+	}
+}
+
+func TestBuildOSC9(t *testing.T) {
+	seq := BuildSequence("osc9", "ignored", "等待输入")
+	want := "\033]9;等待输入\007"
+	if seq != want {
+		t.Fatalf("got %q want %q", seq, want)
+	}
+}
+
+func TestSemicolonInTitleEscaped(t *testing.T) {
+	seq := BuildSequence("osc777", "a;b", "body")
+	if seq != "\033]777;notify;a\\;b;body\007" {
+		t.Fatalf("unexpected escape: %q", seq)
+	}
+}