feat: persist browser sessions and update admin workflows

backend/app/services/scheduler.py

@@ -46,6 +46,7 @@ def _check_upstream(upstream_id: int) -> None:
 
         auth_config = json.loads(upstream.auth_config_json or "{}")
         was_unhealthy = upstream.last_status == "unhealthy"
+        balance_alert_triggered = False
         snapshot = None
         changes = None
 
@@ -76,6 +77,14 @@ def _check_upstream(upstream_id: int) -> None:
                 if balance is not None:
                     upstream.balance = balance
                     upstream.balance_updated_at = datetime.now(timezone.utc)
+                    # ── 余额告警阈值检查 ──
+                    threshold = upstream.balance_alert_threshold
+                    if threshold is not None and threshold > 0:
+                        if balance < threshold and not upstream.balance_alert_notified:
+                            upstream.balance_alert_notified = True
+                            balance_alert_triggered = True
+                        elif balance >= threshold and upstream.balance_alert_notified:
+                            upstream.balance_alert_notified = False
             except Exception as exc:
                 # failure path
                 upstream.consecutive_failures = (upstream.consecutive_failures or 0) + 1
@@ -152,6 +161,12 @@ def _check_upstream(upstream_id: int) -> None:
         _notify_rate_changed(upstream_id, upstream.name, upstream.base_url, changes)
         _sync_website_bindings(upstream_id, changes)
 
+    if balance_alert_triggered:
+        _notify_balance_low(
+            upstream_id, upstream.name, upstream.base_url,
+            upstream.balance, upstream.balance_alert_threshold,
+        )
+
 
 def _notify_status(
     upstream_id: int,
@@ -184,6 +199,22 @@ def _notify_rate_changed(
         db.close()
 
 
+def _notify_balance_low(
+    upstream_id: int,
+    upstream_name: str,
+    base_url: str,
+    balance: float,
+    threshold: float,
+) -> None:
+    db = SessionLocal()
+    try:
+        webhook_service.send_balance_low(db, upstream_id, upstream_name, base_url, balance, threshold)
+    except Exception:
+        logger.exception("balance low webhook failed for upstream %s", upstream_name)
+    finally:
+        db.close()
+
+
 def _sync_upstream_keys(upstream_id: int, snapshot: dict[str, Any], captured_at: datetime) -> None:
     """上游检测成功后同步 SmartUp Key 状态（远端删除/分组删除）。"""
     db = SessionLocal()