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/context/meta.go

@@ -0,0 +1,69 @@
+package context
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+type Meta struct {
+	Agent   string
+	CWD     string
+	Context string
+	Event   string
+}
+
+func Render(tmpl string, m Meta) string {
+	ctx := m.ResolveContext(m.Context)
+	out := strings.ReplaceAll(tmpl, "{agent}", m.Agent)
+	out = strings.ReplaceAll(out, "{context}", ctx)
+	return out
+}
+
+func (m Meta) ResolveContext(window string) string {
+	if window != "" {
+		return window
+	}
+	if m.Context != "" {
+		return m.Context
+	}
+	cwd := m.CWD
+	if cwd == "" {
+		cwd, _ = os.Getwd()
+	}
+	if cwd == "" {
+		return "unknown"
+	}
+	return filepath.Base(cwd)
+}
+
+func TmuxWindowName() string {
+	if os.Getenv("TMUX") == "" {
+		return ""
+	}
+	out, err := exec.Command("tmux", "display-message", "-p", "#{window_name}").Output()
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(string(out))
+}
+
+func MetaFromEnv(agent, event string) Meta {
+	cwd := os.Getenv("AGENT_NOTIFY_CWD")
+	if cwd == "" {
+		cwd, _ = os.Getwd()
+	}
+	if a := os.Getenv("AGENT_NOTIFY_AGENT"); a != "" {
+		agent = a
+	}
+	if e := os.Getenv("AGENT_NOTIFY_EVENT"); e != "" {
+		event = e
+	}
+	return Meta{
+		Agent:   agent,
+		CWD:     cwd,
+		Context: TmuxWindowName(),
+		Event:   event,
+	}
+}