Add piece_weight calibration: enter Stück + Gramm per delivery, average auto-calculated

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

app/Models/Spice.php

@@ -6,7 +6,7 @@ use Illuminate\Database\Eloquent\Model;
 
 class Spice extends Model
 {
-    protected $fillable = ['name', 'quantity', 'unit'];
+    protected $fillable = ['name', 'quantity', 'unit', 'piece_weight'];
 
     public function recipes()
     {
@@ -24,4 +24,17 @@ class Spice extends Model
     {
         $this->update(['quantity' => $this->stockMovements()->sum('amount')]);
     }
+
+    public function recalculatePieceWeight(): void
+    {
+        $result = SpiceSupplier::where('spice_id', $this->id)
+            ->whereNotNull('weight_g')
+            ->where('weight_g', '>', 0)
+            ->selectRaw('SUM(weight_g) as total_grams, SUM(amount) as total_pieces')
+            ->first();
+
+        if ($result && $result->total_pieces > 0) {
+            $this->update(['piece_weight' => round($result->total_grams / $result->total_pieces, 3)]);
+        }
+    }
 }