fix(cron): fix timezone display bug, add tz validation and skill docs

nanobot/cli/commands.py

@@ -719,17 +719,15 @@ def cron_list(
     table.add_column("Status")
     table.add_column("Next Run")
     
-    import datetime
     import time
+    from datetime import datetime as _dt
     from zoneinfo import ZoneInfo
     for job in jobs:
         # Format schedule
         if job.schedule.kind == "every":
             sched = f"every {(job.schedule.every_ms or 0) // 1000}s"
         elif job.schedule.kind == "cron":
-            sched = job.schedule.expr or ""
-            if job.schedule.tz:
-                sched = f"{sched} ({job.schedule.tz})"
+            sched = f"{job.schedule.expr or ''} ({job.schedule.tz})" if job.schedule.tz else (job.schedule.expr or "")
         else:
             sched = "one-time"
         
@@ -737,13 +735,10 @@ def cron_list(
         next_run = ""
         if job.state.next_run_at_ms:
             ts = job.state.next_run_at_ms / 1000
-            if job.schedule.kind == "cron" and job.schedule.tz:
-                try:
-                    dt = datetime.fromtimestamp(ts, ZoneInfo(job.schedule.tz))
-                    next_run = dt.strftime("%Y-%m-%d %H:%M")
-                except Exception:
-                    next_run = time.strftime("%Y-%m-%d %H:%M", time.localtime(ts))
-            else:
+            try:
+                tz = ZoneInfo(job.schedule.tz) if job.schedule.tz else None
+                next_run = _dt.fromtimestamp(ts, tz).strftime("%Y-%m-%d %H:%M")
+            except Exception:
                 next_run = time.strftime("%Y-%m-%d %H:%M", time.localtime(ts))
         
         status = "[green]enabled[/green]" if job.enabled else "[dim]disabled[/dim]"