fix: add missing spaces in cron prompt and replace deprecated utcnow() (#6192)

1. Fix missing spaces in cron job wake prompt string concatenation.
   Python implicit string concatenation produced:
   "...scheduled taskProceed..." and "...conversation.After..."
   which sent garbled instructions to the LLM agent, causing unreliable
   cron job execution.

2. Replace deprecated datetime.utcnow() with
   datetime.now(datetime.timezone.utc) in JWT generation.
   utcnow() is deprecated since Python 3.12 and returns naive datetime
   which can cause incorrect token expiry on non-UTC systems.

Closes #6103
Closes #6165

Co-authored-by: easonysliu <easonysliu@tencent.com>

astrbot/core/cron/manager.py

@@ -332,9 +332,9 @@ class CronJobManager:
             cron_job=cron_job_str
         )
         req.prompt = (
-            "You are now responding to a scheduled task"
+            "You are now responding to a scheduled task. "
             "Proceed according to your system instructions. "
-            "Output using same language as previous conversation."
+            "Output using same language as previous conversation. "
             "After completing your task, summarize and output your actions and results."
         )
         if not req.func_tool:

astrbot/dashboard/routes/auth.py

@@ -82,7 +82,7 @@ class AuthRoute(Route):
     def generate_jwt(self, username):
         payload = {
             "username": username,
-            "exp": datetime.datetime.utcnow() + datetime.timedelta(days=7),
+            "exp": datetime.datetime.now(datetime.timezone.utc) + datetime.timedelta(days=7),
         }
         jwt_token = self.config["dashboard"].get("jwt_secret", None)
         if not jwt_token: