feat: import agents_and_robots platform as unibots (Matrix-out, unibus transport)

Reemplaza el scaffold del echobot por la plataforma completa de bots traida
desde ~/DataProyects/Github/agents_and_robots tras la operacion Matrix-out:
los bots ya no hablan por Matrix sino por el bus unibus (modelo todo-rooms +
E2E via shell/transportunibus sobre github.com/enmanuel/unibus/pkg/client).

- go.mod: replace de unibus -> ../unibus y de fn-registry -> ../../../.. (paths
  relativos reajustados a la nueva ubicacion dentro de fn_registry).
- app.md: bump a 0.2.0, descripcion + arquitectura + comandos + gotchas reales.
- modulo Go conservado como github.com/enmanuel/agents (sin reescribir imports).

agents_and_robots queda archivado como museo de la era Matrix.

shell/bus/bus_test.go

@@ -0,0 +1,91 @@
+package bus_test
+
+import (
+	"log/slog"
+	"testing"
+
+	"github.com/enmanuel/agents/shell/bus"
+)
+
+func newBus() *bus.Bus {
+	return bus.New(slog.Default())
+}
+
+func TestSubscribeAndSend(t *testing.T) {
+	b := newBus()
+	ch := b.Subscribe("agent-a")
+
+	msg := bus.AgentMessage{From: "orch", To: "agent-a", Kind: bus.KindTask, Payload: map[string]string{"k": "v"}}
+	if err := b.Send(msg); err != nil {
+		t.Fatalf("Send: %v", err)
+	}
+
+	got := <-ch
+	if got.Kind != bus.KindTask || got.Payload["k"] != "v" {
+		t.Fatalf("unexpected message: %+v", got)
+	}
+}
+
+func TestUnsubscribeClosesChannel(t *testing.T) {
+	b := newBus()
+	ch := b.Subscribe("agent-b")
+
+	b.Unsubscribe("agent-b")
+
+	// Channel must be closed — reading from a closed channel returns zero value + ok=false.
+	_, ok := <-ch
+	if ok {
+		t.Fatal("expected channel to be closed after Unsubscribe")
+	}
+}
+
+func TestUnsubscribeRemovesFromBus(t *testing.T) {
+	b := newBus()
+	b.Subscribe("agent-c")
+	b.Unsubscribe("agent-c")
+
+	// Sending after unsubscribe must return an error, not panic.
+	err := b.Send(bus.AgentMessage{To: "agent-c", Kind: "ping"})
+	if err == nil {
+		t.Fatal("expected error when sending to unsubscribed agent")
+	}
+}
+
+func TestUnsubscribeIdempotent(t *testing.T) {
+	b := newBus()
+	b.Subscribe("agent-d")
+	// Double unsubscribe must not panic.
+	b.Unsubscribe("agent-d")
+	b.Unsubscribe("agent-d")
+}
+
+func TestUnsubscribeNonExistent(t *testing.T) {
+	b := newBus()
+	// Unsubscribing an ID that was never subscribed must not panic.
+	b.Unsubscribe("does-not-exist")
+}
+
+func TestSendToUnknownAgent(t *testing.T) {
+	b := newBus()
+	err := b.Send(bus.AgentMessage{To: "ghost", Kind: "hello"})
+	if err == nil {
+		t.Fatal("expected error when sending to unknown agent")
+	}
+}
+
+func TestResubscribeAfterUnsubscribe(t *testing.T) {
+	b := newBus()
+	b.Subscribe("agent-e")
+	b.Unsubscribe("agent-e")
+
+	// Re-subscribe must work and deliver messages.
+	ch2 := b.Subscribe("agent-e")
+	msg := bus.AgentMessage{To: "agent-e", Kind: "ping"}
+	if err := b.Send(msg); err != nil {
+		t.Fatalf("Send after re-subscribe: %v", err)
+	}
+	got := <-ch2
+	if got.Kind != "ping" {
+		t.Fatalf("unexpected kind: %q", got.Kind)
+	}
+}