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/install/install_test.go

@@ -0,0 +1,44 @@
+package install
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestMergeCursorHooks(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "hooks.json")
+	existing := `{"version":1,"hooks":{"beforeShellExecution":[{"command":"other"}]}}`
+	os.WriteFile(path, []byte(existing), 0644)
+
+	if err := MergeCursorHooks(path, false); err != nil {
+		t.Fatal(err)
+	}
+	data, _ := os.ReadFile(path)
+	var doc map[string]any
+	json.Unmarshal(data, &doc)
+	hooks := doc["hooks"].(map[string]any)
+	stop := hooks["stop"].([]any)
+	if len(stop) != 1 {
+		t.Fatalf("expected stop hook added")
+	}
+}
+
+func TestMergeCursorHooksNoOverwrite(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "hooks.json")
+	existing := `{"version":1,"hooks":{"stop":[{"command":"existing"}]}}`
+	os.WriteFile(path, []byte(existing), 0644)
+	MergeCursorHooks(path, false)
+	data, _ := os.ReadFile(path)
+	var doc map[string]any
+	json.Unmarshal(data, &doc)
+	hooks := doc["hooks"].(map[string]any)
+	stop := hooks["stop"].([]any)
+	entry := stop[0].(map[string]any)
+	if entry["command"] != "existing" {
+		t.Fatal("should not overwrite existing stop hook without force")
+	}
+}