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/Models/Batch.php

@@ -38,58 +38,62 @@ class Batch extends Model
 
     protected static function booted(): void
     {
-        // Auto-calculate quantity_g before saving
         static::saving(function (Batch $batch) {
             if ($batch->units_produced && $batch->size_id) {
-                $gramsPerUnit = $batch->size?->packing?->size ?? 0;
-                $batch->quantity_g = $batch->units_produced * $gramsPerUnit;
+                $batch->quantity_g = $batch->units_produced * ($batch->size?->packing?->size ?? 0);
             }
         });
 
         static::created(function (Batch $batch) {
-            $batch->deductSpices();
+            $batch->writeSpiceMovements();
         });
 
         static::updated(function (Batch $batch) {
             if ($batch->wasChanged(['recipe_id', 'size_id', 'units_produced'])) {
-                $batch->restoreSpices(
-                    $batch->getOriginal('recipe_id'),
-                    $batch->getOriginal('quantity_g'),
-                );
-                $batch->deductSpices();
+                $batch->deleteSpiceMovements();
+                $batch->writeSpiceMovements();
             }
         });
 
         static::deleting(function (Batch $batch) {
-            $batch->restoreSpices($batch->recipe_id, $batch->quantity_g);
+            $batch->deleteSpiceMovements();
         });
     }
 
-    private function deductSpices(): void
+    private function writeSpiceMovements(): void
     {
         if (! $this->quantity_g || ! $this->recipe_id) {
             return;
         }
 
         $recipe = Recipe::with('spices')->find($this->recipe_id);
-
-        foreach ($recipe->spices as $spice) {
-            $grams = $this->quantity_g * $spice->pivot->amount_in_percent / 100;
-            $spice->decrement('quantity', $grams);
-        }
-    }
-
-    private function restoreSpices(int $recipeId, float $quantityG): void
-    {
-        if (! $quantityG || ! $recipeId) {
+        if (! $recipe) {
             return;
         }
 
-        $recipe = Recipe::with('spices')->find($recipeId);
-
         foreach ($recipe->spices as $spice) {
-            $grams = $quantityG * $spice->pivot->amount_in_percent / 100;
-            $spice->increment('quantity', $grams);
+            $grams = $this->quantity_g * $spice->pivot->amount_in_percent / 100;
+            SpiceStockMovement::create([
+                'spice_id'    => $spice->id,
+                'amount'      => -$grams,
+                'source_type' => 'batch',
+                'source_id'   => $this->id,
+                'description' => 'Charge ' . $this->lot_number . ' (' . $spice->pivot->amount_in_percent . '%)',
+            ]);
+            $spice->recalculateQuantity();
         }
     }
+
+    private function deleteSpiceMovements(): void
+    {
+        $spiceIds = SpiceStockMovement::where('source_type', 'batch')
+            ->where('source_id', $this->id)
+            ->pluck('spice_id');
+
+        SpiceStockMovement::where('source_type', 'batch')
+            ->where('source_id', $this->id)
+            ->delete();
+
+        Spice::whereIn('id', $spiceIds)->get()->each->recalculateQuantity();
+    }
 }