fix(dashboard): improve WebUI disabled messaging

When WebUI is disabled via config, tell users to use the online
dashboard at dash.astrbot.men instead of the cryptic technical message.

When WebUI files are missing (index.html not found), also redirect
users to the online dashboard instead of just saying "WebUI will be
disabled."

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

astrbot/dashboard/server.py

@@ -177,8 +177,8 @@ class AstrBotDashboard:
 
         if self.enable_webui and not (Path(self.data_path) / "index.html").exists():
             logger.warning(
-                f"Dashboard static assets not found: index.html is missing in {self.data_path}. "
-                "WebUI will be disabled."
+                f"找不到内置前端 (index.html missing in {self.data_path})，"
+                "但你可以通过在线面板访问：dash.astrbot.men"
             )
             self.enable_webui = False
 
@@ -473,15 +473,8 @@ class AstrBotDashboard:
 
     async def run(self) -> None:
         """Run dashboard server (blocking)"""
-        logger.info(
-            "[Dashboard] Starting server... enable_webui=%s, ASTRBOT_DASHBOARD_ENABLE=%s",
-            self.enable_webui,
-            os.environ.get("ASTRBOT_DASHBOARD_ENABLE"),
-        )
         if not self.enable_webui:
-            logger.warning(
-                "WebUI 已禁用 (dashboard.enable=false or ASTRBOT_DASHBOARD_ENABLE=false), 但 API 服务器将继续启动"
-            )
+            logger.warning("内置前端已禁用，请访问在线前端面板：dash.astrbot.men")
 
         dashboard_config = self.config.get("dashboard", {})
         host_value = (