feat(meal-plan): add servings field to MealPlanEntry and update related functionality

feat(products): implement bulk update for product categories

feat(recipes): add servings input to WriteRecipePage and update MealPlanClient for servings management

refactor(types): enhance Product and Category types with additional properties

frontend/app/recipes/write/WriteRecipePage.tsx

@@ -42,6 +42,7 @@ export default function WriteRecipePage() {
   const [editedName, setEditedName] = useState('');
   const [editedDescription, setEditedDescription] = useState('');
   const [editedInstructions, setEditedInstructions] = useState('');
+  const [editedServings, setEditedServings] = useState<number | null>(null);
   const [imageUrl, setImageUrl] = useState<string | null>(null);
   const [ingredients, setIngredients] = useState<ParsedIngredientRow[]>([]);
   const [allProducts, setAllProducts] = useState<Product[]>([]);
@@ -180,6 +181,7 @@ export default function WriteRecipePage() {
       description: editedDescription || undefined,
       instructions: editedInstructions || undefined,
       imageUrl: imageUrl || undefined,
+      servings: editedServings ?? undefined,
       ingredients: validIngredients.map((ing) => ({
         productId: ing.selectedProductId,
         quantity: Number(ing.editedQuantity),
@@ -358,6 +360,20 @@ Stek löken i lite smör. Tillsätt köttfärsen...`}</pre>
                   style={{ width: '100%', padding: '0.75rem', border: '1px solid #ddd', borderRadius: '4px', fontSize: '1rem', minHeight: '150px', fontFamily: 'monospace', boxSizing: 'border-box' }}
                 />
               </div>
+
+              <div>
+                <label style={{ display: 'block', marginBottom: '0.5rem', fontWeight: 600 }}>Portioner</label>
+                <input
+                  type="number"
+                  min={1}
+                  step={1}
+                  value={editedServings ?? ''}
+                  onChange={(e) => setEditedServings(e.target.value ? Number(e.target.value) : null)}
+                  placeholder="t.ex. 4"
+                  style={{ width: '120px', padding: '0.5rem 0.75rem', border: '1px solid #ddd', borderRadius: '4px', fontSize: '1rem' }}
+                />
+                <p style={{ fontSize: '0.82rem', color: '#888', margin: '0.3rem 0 0' }}>Anges portioner kan mängderna skalas på receptsidan.</p>
+              </div>
             </div>
 
             {/* Ingredienser */}