refactor: mover tools a subpackages individuales

Cada tool ahora vive en su propio subpackage dentro de tools/ (clock, file,
http, knowledgetools, matrix, memorytools, ssh, weather) en lugar de archivos
planos en el paquete raíz tools/. Esto mejora la organización, permite imports
selectivos y reduce acoplamiento entre tools. El paquete tools/ raíz conserva
los tipos base (Def, Param, Result, ToolFunc, Tool, Registry).

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

tools/clock/clock.go

@@ -0,0 +1,33 @@
+package clock
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/enmanuel/agents/tools"
+)
+
+// NewCurrentTime creates a current_time tool that returns the current date and time.
+// Useful for agents that need temporal awareness.
+func NewCurrentTime() tools.Tool {
+	return tools.Tool{
+		Def: tools.Def{
+			Name:        "current_time",
+			Description: "Returns the current date and time in the server's timezone. Use this when you need to know the current time or date.",
+			Parameters: []tools.Param{
+				{Name: "format", Type: "string", Description: "Optional Go time format string. Defaults to RFC3339 if empty.", Required: false},
+			},
+		},
+		Exec: func(ctx context.Context, args map[string]any) tools.Result {
+			layout := tools.GetString(args, "format")
+			if layout == "" {
+				layout = time.RFC3339
+			}
+
+			now := time.Now()
+			output := fmt.Sprintf("Current time: %s\nTimezone: %s", now.Format(layout), now.Location().String())
+			return tools.Result{Output: output}
+		},
+	}
+}