feat: añadir agentes wikipedia-bot y exchange-bot

wikipedia-bot: agente GPT-4o con tool wikipedia_search para consultar
información de Wikipedia. Responde en español, tono profesional.

exchange-bot: agente GPT-4o con 4 tools de exchange rate para consultar
tasas de cambio, convertir entre monedas, listar monedas disponibles
y ver historial. Requiere EXCHANGERATE_API_KEY en .env.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agents/exchange-bot/agent.go

@@ -0,0 +1,29 @@
+// Package exchange implements the exchange-bot agent for currency exchange rate queries.
+// Rules are pure: no I/O, no side effects.
+package exchange
+
+import (
+	"github.com/enmanuel/agents/devagents"
+	"github.com/enmanuel/agents/pkg/decision"
+)
+
+func init() {
+	devagents.Register("exchange-bot", Rules)
+}
+
+// Rules returns the decision rules for exchange-bot.
+// Any direct message or mention is forwarded to the LLM with exchange rate tools.
+func Rules() []decision.Rule {
+	return []decision.Rule{
+		{
+			Name: "llm-all",
+			Match: func(ctx decision.MessageContext) bool {
+				return ctx.IsDirectMsg || ctx.IsMention
+			},
+			Actions: []decision.Action{{
+				Kind: decision.ActionKindLLM,
+				LLM:  &decision.LLMAction{},
+			}},
+		},
+	}
+}