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/transportunibus/demo.go

@@ -0,0 +1,35 @@
+package transportunibus
+
+import (
+	"context"
+	"log/slog"
+	"strings"
+
+	"github.com/enmanuel/agents/pkg/transport"
+)
+
+// DemoEchoHandler returns a minimal bot handler that proves the unibus transport
+// end to end: it receives a neutral InboundMessage and answers in the same room.
+// It echoes the message body back as a reply, with one built-in command
+// (!ping → pong) to show command routing works over the bus. It is intentionally
+// tiny — the point is the transport, not the bot.
+func DemoEchoHandler(t transport.Transport, logger *slog.Logger) transport.Handler {
+	if logger == nil {
+		logger = slog.Default()
+	}
+	return func(ctx context.Context, in transport.InboundMessage) {
+		reply := "echo: " + in.Body
+		if strings.TrimSpace(in.Body) == "!ping" {
+			reply = "pong"
+		}
+		out := transport.OutboundReply{
+			RoomID:   in.RoomID,
+			ReplyTo:  in.MsgID,
+			ThreadID: in.ThreadID,
+			Markdown: reply,
+		}
+		if err := t.Reply(ctx, out); err != nil {
+			logger.Error("demo echo reply failed", "err", err, "sender", in.SenderID)
+		}
+	}
+}