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/transport/flags.go

@@ -0,0 +1,57 @@
+package transport
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+// Kind identifies which messaging fabric a bot runs on.
+type Kind string
+
+const (
+	// KindMatrix is the proven Matrix (mautrix) path — the default, so master
+	// stays on the battle-tested transport.
+	KindMatrix Kind = "matrix"
+	// KindUnibus routes the bot over the unibus message bus.
+	KindUnibus Kind = "unibus"
+)
+
+// Select chooses a bot's transport. unibus is used only when the global feature
+// flag is enabled AND the bot has opted in; otherwise Matrix. This is the
+// branch-by-abstraction toggle: with the flag on, bots migrate to unibus one at
+// a time by opting in, while every other bot keeps speaking Matrix unchanged.
+func Select(flagEnabled, botOptIn bool) Kind {
+	if flagEnabled && botOptIn {
+		return KindUnibus
+	}
+	return KindMatrix
+}
+
+// flagsFile mirrors dev/feature_flags.json (see .claude rule feature_flags.md).
+type flagsFile struct {
+	Flags map[string]struct {
+		Enabled     bool   `json:"enabled"`
+		Issue       string `json:"issue"`
+		Description string `json:"description"`
+	} `json:"flags"`
+}
+
+// FlagEnabled reports whether the named feature flag is enabled in the given
+// dev/feature_flags.json file. A missing file or missing flag reads as false
+// (fail-safe: default to the Matrix path), not an error — only malformed JSON
+// surfaces an error.
+func FlagEnabled(path, name string) (bool, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return false, nil
+		}
+		return false, fmt.Errorf("transport: read flags %q: %w", path, err)
+	}
+	var f flagsFile
+	if err := json.Unmarshal(data, &f); err != nil {
+		return false, fmt.Errorf("transport: parse flags %q: %w", path, err)
+	}
+	return f.Flags[name].Enabled, nil
+}