fix feed initial balance and report button

backend/apps/operations/services/feed_sacks.py

@@ -0,0 +1,32 @@
+from __future__ import annotations
+
+from datetime import date
+
+from apps.farms.models import Cycle
+from apps.operations.models import FeedSacks
+
+
+def recompute_feed_sack_in_totals(cycle: Cycle) -> None:
+    """Rebuild cumulative in_total from the cycle opening balance plus daily IoT in."""
+    running = cycle.feed_initial_balance
+    for fs_row in FeedSacks.objects.filter(cycle=cycle).order_by("date", "pk"):
+        running += fs_row.in_today
+        if fs_row.in_total != running:
+            fs_row.in_total = running
+            fs_row.save(update_fields=["in_total", "updated_at"])
+
+
+def ensure_opening_feed_sack_snapshot(cycle: Cycle, balance_date: date) -> FeedSacks | None:
+    """Seed a zero-activity snapshot when opening balance is saved before any IoT sync."""
+    if FeedSacks.objects.filter(cycle=cycle).exists():
+        return None
+    return FeedSacks.objects.create(
+        cycle=cycle,
+        date=balance_date,
+        in_today=0,
+        out_today=0,
+        in_total=cycle.feed_initial_balance,
+        out_total=0,
+        feed_use_today=0,
+        feed_use_total=0,
+    )