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/config/config_test.go

@@ -0,0 +1,63 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestDefaultConfig(t *testing.T) {
+	cfg := Default()
+	if !cfg.Events.Stop {
+		t.Fatal("expected stop=true by default")
+	}
+	if cfg.Events.Idle {
+		t.Fatal("expected idle=false by default")
+	}
+	if cfg.Notify.Protocol != "osc777" {
+		t.Fatalf("expected osc777, got %q", cfg.Notify.Protocol)
+	}
+}
+
+func TestLoadFromFile(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.toml")
+	content := `
+[events]
+stop = false
+tool = true
+
+[notify]
+body_stop = "custom stop"
+`
+	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := Load(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cfg.Events.Stop {
+		t.Fatal("expected stop=false")
+	}
+	if !cfg.Events.Tool {
+		t.Fatal("expected tool=true")
+	}
+	if cfg.Notify.BodyStop != "custom stop" {
+		t.Fatalf("got %q", cfg.Notify.BodyStop)
+	}
+}
+
+func TestEventEnabled(t *testing.T) {
+	cfg := Default()
+	if !cfg.EventEnabled("stop") {
+		t.Fatal("expected stop enabled by default")
+	}
+	if !cfg.EventEnabled("STOP") {
+		t.Fatal("expected case-insensitive match")
+	}
+	cfg.Events.Stop = false
+	if cfg.EventEnabled("stop") {
+		t.Fatal("expected stop disabled")
+	}
+}