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.

pkg/security/groups.go

@@ -0,0 +1,17 @@
+// Package security provides pure types and functions for centralized permission management.
+// No I/O, no side effects — only data transformations.
+package security
+
+// UserGroup is a named set of Matrix user IDs.
+// Members may contain "*" to represent all users.
+type UserGroup struct {
+	Name    string
+	Members []string
+}
+
+// AgentGroup is a named set of agent IDs.
+// Agents may contain "*" to represent all agents.
+type AgentGroup struct {
+	Name   string
+	Agents []string
+}