Warenwirtschaft: AP-09 bis AP-13 (Produktbestand, Set-Produkte, Ausschuss, Konzepte)

- AP-09 Produktbestand inkl. Bewegungshistorie (product_stock_movements, ProductStockService)
- AP-10 Rohstoffbestand-Ansicht je Lager (RawMaterialStockController)
- AP-11 Bestandsschwellen / Out-of-Stock-Handling fuer Produkte und Shop
- AP-12 Ausgang/Ausschuss (stock_disposals, StockDisposalController, InventoryService)
- Set-Produkte (product_set_items) inkl. Aufloesung
- Produktentwicklung & Hinweise-Verwaltung (Notices)
- AP-13 Entwicklungskonzept Shop-Bestandsabzug im Plan dokumentiert
- Feature-Tests fuer neue Module + aktualisierter Entwicklungsplan

Co-authored-by: Cursor <cursoragent@cursor.com>

app/Models/ProductStockMovement.php

@@ -0,0 +1,70 @@
+<?php
+
+namespace App\Models;
+
+use App\User;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+
+class ProductStockMovement extends Model
+{
+    protected $fillable = [
+        'product_id',
+        'direction',
+        'quantity',
+        'reason',
+        'source',
+        'note',
+        'user_id',
+        'reference_type',
+        'reference_id',
+    ];
+
+    /**
+     * @return array<string, string>
+     */
+    protected function casts(): array
+    {
+        return [
+            'quantity' => 'integer',
+        ];
+    }
+
+    /**
+     * @return BelongsTo<Product, $this>
+     */
+    public function product(): BelongsTo
+    {
+        return $this->belongsTo(Product::class);
+    }
+
+    /**
+     * @return BelongsTo<User, $this>
+     */
+    public function user(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    /**
+     * @return MorphTo<Model, $this>
+     */
+    public function reference(): MorphTo
+    {
+        return $this->morphTo();
+    }
+
+    public function isIn(): bool
+    {
+        return $this->direction === 'in';
+    }
+
+    /**
+     * Vorzeichenbehaftete Menge (Eingang positiv, Ausgang negativ).
+     */
+    public function signedQuantity(): int
+    {
+        return $this->isIn() ? (int) $this->quantity : -(int) $this->quantity;
+    }
+}