Created Turnpike, event attendee and volunteer management

Built after prototype, Traverse, an attendee and volunteer list
maintainer.

broker.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"encoding/json"
+	"sync"
+)
+
+// Broker is a simple in-memory pub/sub for SSE events.
+type Broker struct {
+	mu      sync.Mutex
+	clients map[chan []byte]struct{}
+}
+
+func newBroker() *Broker {
+	return &Broker{clients: make(map[chan []byte]struct{})}
+}
+
+func (b *Broker) subscribe() chan []byte {
+	ch := make(chan []byte, 8)
+	b.mu.Lock()
+	b.clients[ch] = struct{}{}
+	b.mu.Unlock()
+	return ch
+}
+
+func (b *Broker) unsubscribe(ch chan []byte) {
+	b.mu.Lock()
+	delete(b.clients, ch)
+	b.mu.Unlock()
+	close(ch)
+}
+
+func (b *Broker) publish(event string, data any) {
+	payload, _ := json.Marshal(map[string]any{"event": event, "data": data})
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	for ch := range b.clients {
+		select {
+		case ch <- payload:
+		default:
+		}
+	}
+}