fix(ume): global clear-push setting, schema migration, and help hints

Make forward-on-clear a global monitor toggle, run key-alert DDL in an
isolated startup transaction, and fix HelpHint popovers plus API errors
when the server returns non-JSON responses.

Co-authored-by: Cursor <cursoragent@cursor.com>

netx_api/models.py

@@ -201,6 +201,16 @@ class UmeAlarmHistory(Base):
     raw_json: Mapped[str] = mapped_column(Text, default="{}")
 
 
+class UmeKeyAlertMonitorConfig(Base):
+    """Global monitor options for key alert forwarding (singleton row id=1)."""
+
+    __tablename__ = "ume_key_alert_monitor_config"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True)
+    forward_on_clear: Mapped[int] = mapped_column(Integer, default=0)
+    updated_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow, index=True)
+
+
 class UmeKeyAlertRule(Base):
     """Key alert rule matched by UME notificationId or alarm description keyword."""