refactor(tools): remove duplicate truncate functions and add docs

- Remove duplicate truncate/truncateString functions from loop.go and cron.go
- Use utils.Truncate consistently across codebase
- Add Workspace Layout section to README
- Document cron/scheduled tasks functionality

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

pkg/tools/cron.go

@@ -8,15 +8,9 @@ import (
 
 	"github.com/sipeed/picoclaw/pkg/bus"
 	"github.com/sipeed/picoclaw/pkg/cron"
+	"github.com/sipeed/picoclaw/pkg/utils"
 )
 
-func truncateString(s string, maxLen int) string {
-	if len(s) <= maxLen {
-		return s
-	}
-	return s[:maxLen]
-}
-
 // JobExecutor is the interface for executing cron jobs through the agent
 type JobExecutor interface {
 	ProcessDirectWithChannel(ctx context.Context, content, sessionKey, channel, chatID string) (string, error)
@@ -171,8 +165,11 @@ func (t *CronTool) addJob(args map[string]interface{}) (string, error) {
 		deliver = d
 	}
 
+	// Truncate message for job name (max 30 chars)
+	messagePreview := utils.Truncate(message, 30)
+
 	job, err := t.cronService.AddJob(
-		truncateString(message, 30),
+		messagePreview,
 		schedule,
 		message,
 		deliver,