feat: add asistente-2 agent with tool-use and E2EE verification

Nuevo agente asistente-2 con herramienta current_time habilitada para
demostrar el flujo completo de tool-use (LLM → tool call → resultado → respuesta).

Incluye:
- agents/asistente2/: reglas puras, config con tool_use.enabled, system prompt
- tools/time.go: herramienta current_time (siempre disponible para todos los agentes)
- cmd/verify/: comando para subir cross-signing keys y eliminar el warning
  "Encrypted by a device not verified by its owner"
- Registro en runtime.go (current_time) y launcher/main.go (rulesRegistry)

El cmd/verify usa mautrix GenerateAndUploadCrossSigningKeysWithPassword
para configurar cross-signing via UIA con la password del bot.

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

tools/time.go

@@ -0,0 +1,31 @@
+package tools
+
+import (
+	"context"
+	"fmt"
+	"time"
+)
+
+// NewCurrentTime creates a current_time tool that returns the current date and time.
+// Useful for agents that need temporal awareness.
+func NewCurrentTime() Tool {
+	return Tool{
+		Def: 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: []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) Result {
+			layout := 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 Result{Output: output}
+		},
+	}
+}