Introduce spice_stock_movements ledger for traceable stock changes

Every delivery and batch now writes a signed movement entry instead of
directly incrementing/decrementing spice.quantity. The balance is always
the sum of all movements. Existing data is backfilled in the migration.
Rohstoff edit page shows the full movement history (Lagerbewegungen tab).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Filament/User/Resources/SpiceResource.php

@@ -78,7 +78,7 @@ class SpiceResource extends Resource
     public static function getRelations(): array
     {
         return [
-            //
+            RelationManagers\StockMovementsRelationManager::class,
         ];
     }