feat: añadir tools wikipedia_search y exchange_rate

- tools/wikipedia/wikipedia.go: tool wikipedia_search que consulta la
  API pública de Wikipedia (sin auth). Devuelve resumen del artículo.
- tools/exchange/exchange.go: 4 tools de tipo de cambio usando
  exchangerate-api.com: exchange_rate_get, exchange_rate_convert,
  exchange_rate_list, exchange_rate_historical.
- internal/config/schema.go: añadir ExchangeRateToolCfg con Enabled,
  APIKey, APIKeyEnv y Timeout.
- devagents/registry_build.go: registrar ambas tool families.
  wikipedia_search siempre disponible; exchange rate tools requieren
  APIKey configurado (deny-by-default con WARN si falta).
- devagents/registry_build_test.go: actualizar test de registry build.

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

devagents/registry_build.go

@@ -25,6 +25,8 @@ import (
 	toolskills "github.com/enmanuel/agents/tools/skilltools"
 	toolssh "github.com/enmanuel/agents/tools/ssh"
 	toolweather "github.com/enmanuel/agents/tools/weather"
+	toolwikipedia "github.com/enmanuel/agents/tools/wikipedia"
+	toolexchange  "github.com/enmanuel/agents/tools/exchange"
 
 	"github.com/enmanuel/agents/shell/matrix"
 )
@@ -187,12 +189,41 @@ func buildToolRegistry(
 	reg.Register(toolweather.NewWeather())
 	logger.Debug("registered weather tool")
 
+	// wikipedia_search tool is always available
+	reg.Register(toolwikipedia.NewWikipediaSearch())
+	logger.Debug("registered wikipedia_search tool")
+
 	// imdb tool (enabled via config)
 	if cfg.Tools.IMDb.Enabled {
 		reg.Register(toolimdb.NewIMDbSearch(cfg.Tools.IMDb))
 		logger.Debug("registered imdb tool")
 	}
 
+	// exchange rate tools (enabled via config)
+	if cfg.Tools.ExchangeRate.Enabled {
+		if t, err := toolexchange.NewExchangeRateGet(cfg.Tools.ExchangeRate); err != nil {
+			logger.Warn("exchange_rate_get disabled: API key not configured", "err", err)
+		} else {
+			reg.Register(t)
+		}
+		if t, err := toolexchange.NewExchangeRateConvert(cfg.Tools.ExchangeRate); err != nil {
+			logger.Warn("exchange_rate_convert disabled: API key not configured", "err", err)
+		} else {
+			reg.Register(t)
+		}
+		if t, err := toolexchange.NewExchangeRateList(cfg.Tools.ExchangeRate); err != nil {
+			logger.Warn("exchange_rate_list disabled: API key not configured", "err", err)
+		} else {
+			reg.Register(t)
+		}
+		if t, err := toolexchange.NewExchangeRateHistorical(cfg.Tools.ExchangeRate); err != nil {
+			logger.Warn("exchange_rate_historical disabled: API key not configured", "err", err)
+		} else {
+			reg.Register(t)
+		}
+		logger.Debug("registered exchange rate tools")
+	}
+
 	// matrix_send is always available
 	reg.Register(toolmatrix.NewMatrixSend(matrixClient, cfg.Tools.Matrix))
 	logger.Debug("registered matrix tool")

devagents/registry_build_test.go

@@ -143,8 +143,8 @@ func TestBuildToolRegistry_ToolCount(t *testing.T) {
 
 	reg := buildToolRegistry(cfg, nil, nil, nil, nil, nil, nil, nil, nil, roomCtx, logger)
 
-	// 3 always-on + 2 HTTP + 1 SSH + 5 file + 1 IMDb = 12
-	expected := 12
+	// 4 always-on (current_time, get_weather, wikipedia_search, matrix_send) + 2 HTTP + 1 SSH + 5 file + 1 IMDb = 13
+	expected := 13
 	if got := reg.Len(); got != expected {
 		t.Errorf("expected %d tools, got %d: %v", expected, got, reg.Names())
 	}