fix finance balance delta recharges

backend/app/models/snapshot.py

@@ -1,5 +1,5 @@
 from datetime import datetime, timezone
-from sqlalchemy import Index, Integer, Text, DateTime, ForeignKey, text
+from sqlalchemy import Float, Index, Integer, Text, DateTime, ForeignKey, text
 from sqlalchemy.orm import mapped_column, Mapped
 from app.database import Base
 
@@ -15,3 +15,16 @@ class UpstreamRateSnapshot(Base):
     __table_args__ = (
         Index("ix_snapshot_upstream_captured", "upstream_id", text("captured_at DESC")),
     )
+
+
+class UpstreamBalanceSnapshot(Base):
+    __tablename__ = "upstream_balance_snapshots"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, index=True)
+    upstream_id: Mapped[int] = mapped_column(Integer, ForeignKey("upstreams.id", ondelete="CASCADE"), index=True)
+    balance: Mapped[float] = mapped_column(Float, nullable=False)
+    captured_at: Mapped[datetime] = mapped_column(DateTime, default=lambda: datetime.now(timezone.utc), index=True)
+
+    __table_args__ = (
+        Index("ix_balance_snap_upstream_captured", "upstream_id", text("captured_at DESC")),
+    )