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/SpiceSupplier.php

@@ -18,7 +18,6 @@ class SpiceSupplier extends Model
         'supplied_at',
     ];
 
-    // Beziehungen
     public function spice()
     {
         return $this->belongsTo(Spice::class);
@@ -28,4 +27,25 @@ class SpiceSupplier extends Model
     {
         return $this->belongsTo(Supplier::class);
     }
+
+    protected static function booted(): void
+    {
+        static::created(function (SpiceSupplier $ss) {
+            SpiceStockMovement::create([
+                'spice_id'    => $ss->spice_id,
+                'amount'      => $ss->amount,
+                'source_type' => 'delivery',
+                'source_id'   => $ss->id,
+                'description' => 'Lieferung' . ($ss->supplier ? ' von ' . $ss->supplier->name : ''),
+            ]);
+            $ss->spice->recalculateQuantity();
+        });
+
+        static::deleted(function (SpiceSupplier $ss) {
+            SpiceStockMovement::where('source_type', 'delivery')
+                ->where('source_id', $ss->id)
+                ->delete();
+            $ss->spice->recalculateQuantity();
+        });
+    }
 }