feat(auth): implement user authentication with JWT and NextAuth

- Added user registration and login functionality with JWT authentication.
- Created auth controller, service, and module in the backend.
- Implemented user model and user products management.
- Integrated NextAuth for session management on the frontend.
- Added middleware for protecting routes and handling public access.
- Updated frontend API routes to include authorization headers.
- Enhanced recipe and user product models to support ownership and visibility.
- Created registration and login pages in the frontend.
- Added necessary types for NextAuth session management.

frontend/app/recipes/[id]/RecipeDetailClient.tsx

@@ -79,6 +79,7 @@ export default function RecipeDetailClient({ recipe: initialRecipe }: { recipe:
     instructions: initialRecipe.instructions || '',
     imageUrl: initialRecipe.imageUrl || '',
     servings: initialRecipe.servings as number | null,
+    isPublic: initialRecipe.isPublic,
     ingredients: initialRecipe.ingredients.map((ing) => ({
       productId: ing.productId,
       quantity: String(ing.quantity),
@@ -469,6 +470,23 @@ export default function RecipeDetailClient({ recipe: initialRecipe }: { recipe:
           </p>
         </section>
 
+        {/* Synlighet */}
+        <section style={sectionStyle}>
+          <h2 style={sectionTitle}>Synlighet</h2>
+          <label style={{ display: 'flex', alignItems: 'center', gap: '0.5rem', cursor: 'pointer' }}>
+            <input
+              type="checkbox"
+              checked={form.isPublic}
+              onChange={(e) => setForm((f) => ({ ...f, isPublic: e.target.checked }))}
+              style={{ width: 16, height: 16 }}
+            />
+            <span>Publikt recept (synligt för alla inloggade)</span>
+          </label>
+          <p style={{ fontSize: '0.85rem', color: '#666', marginTop: '0.4rem', marginBottom: 0 }}>
+            Privata recept syns bara för dig och de du delar med.
+          </p>
+        </section>
+
         {/* Ingredienser */}
         <section style={sectionStyle}>
           <h2 style={sectionTitle}>Ingredienser</h2>