feat(backend): demo seeder, receipt allocations in expand, FOUND ceiling guard

- tools/seed.py: wipes app tables and seeds a clean realistic demo (3
  projects x 2 warehouses, 4 suppliers, 12 materials across all 8 topic
  categories, 4 quotes covering offered / in-transit / partial / completed
  with receipts + matching stock); user roles bound to Casdoor identities
  by username (seed_casdoor.py first)
- expand_service: the line-item receipt aggregate now carries the warehouse
  allocations (target warehouse per received part) for the ledger's
  «رسید شده» split
- inventory_service: FOUND («پیدا شده») is guarded so recovery cannot exceed
  the missing balance for the same (warehouse, material, brand, specs) —
  422 with the remaining balance; STOCK_COUNT semantics unchanged (absolute
  counted qty, auto-diff)

backend/app/services/inventory_service.py

@@ -36,7 +36,7 @@ from app.models.inventory import (
     Warehouse,
 )
 from app.schemas.inventory import InventoryTransactionCreate
-from app.utils.errors import NotFoundError, ValidationError
+from app.utils.errors import AppError, NotFoundError, ValidationError
 
 
 def canonical_specs_hash(specs: dict | None) -> str:
@@ -79,6 +79,39 @@ async def _find_inventory(
     return await db.scalar(stmt)
 
 
+async def _missing_balance(
+    db: AsyncSession,
+    warehouse_id,
+    material_id,
+    brand_id,
+    specs_hash: str,
+) -> Decimal:
+    """Remaining missing balance for (warehouse, material, brand, specs):
+    Σ|LOSS| − ΣFOUND over the transactions of the matching inventory rows."""
+    from sqlalchemy import func
+
+    rows = (
+        await db.execute(
+            select(
+                InventoryTransaction.transaction_type,
+                func.sum(InventoryTransaction.quantity),
+            )
+            .join(InventoryItem, InventoryItem.id == InventoryTransaction.inventory_id)
+            .where(
+                InventoryItem.warehouse_id == warehouse_id,
+                InventoryItem.material_id == material_id,
+                InventoryItem.brand_id.is_(None) if brand_id is None
+                else InventoryItem.brand_id == brand_id,
+                InventoryItem.specs_hash == specs_hash,
+                InventoryTransaction.transaction_type.in_(["LOSS", "FOUND"]),
+            )
+            .group_by(InventoryTransaction.transaction_type)
+        )
+    ).all()
+    totals = {t: (abs(q) if q is not None else Decimal("0")) for t, q in rows}
+    return totals.get("LOSS", Decimal("0")) - totals.get("FOUND", Decimal("0"))
+
+
 async def _get_or_create_inventory(
     db: AsyncSession,
     warehouse_id,
@@ -233,6 +266,19 @@ async def apply_transaction(
 
     # Increasing types: find-or-create the row, then add.
     if t in INCREASING_TYPES:
+        # FOUND («پیدا شده») ceiling: recovery must not exceed the recorded
+        # missing balance for the same (warehouse, material, brand, specs).
+        if t == "FOUND":
+            missing = await _missing_balance(
+                db, payload.warehouse_id, payload.material_id, payload.brand_id, specs_hash
+            )
+            if quantity > missing:
+                raise AppError(
+                    422,
+                    "VALIDATION_ERROR",
+                    f"تعداد پیداشده نمی‌تواند بیشتر از مقدار مفقودی باشد (مانده‌ی مفقودی: {missing})",
+                    field="quantity",
+                )
         row = await _get_or_create_inventory(
             db, payload.warehouse_id, payload.material_id, payload.brand_id,
             payload.unit_id, specs, specs_hash,