feat: scaffold agentmon services and k8s deploy

Adds Go microservices (ingest-gateway, event-processor, query-api, web-ui), NATS+Postgres wiring, initial schema/init job, ingress manifests for LAN+tailnet, and a multi-arch image build script.

internal/queue/nats/subscribe.go

@@ -0,0 +1,41 @@
+package nats
+
+import (
+	"context"
+
+	gnats "github.com/nats-io/nats.go"
+)
+
+type Subscriber struct {
+	conn  *gnats.Conn
+	sub   *gnats.Subscription
+	topic string
+}
+
+func NewSubscriber(url, topic string) (*Subscriber, error) {
+	conn, err := gnats.Connect(url)
+	if err != nil {
+		return nil, err
+	}
+	return &Subscriber{conn: conn, topic: topic}, nil
+}
+
+func (s *Subscriber) Close() {
+	if s.sub != nil {
+		_ = s.sub.Unsubscribe()
+	}
+	s.conn.Close()
+}
+
+func (s *Subscriber) Subscribe(ctx context.Context, handler func(msg []byte) error) error {
+	sub, err := s.conn.Subscribe(s.topic, func(m *gnats.Msg) {
+		_ = handler(m.Data)
+	})
+	if err != nil {
+		return err
+	}
+	s.sub = sub
+
+	<-ctx.Done()
+	return ctx.Err()
+}