Implement health check service and global exception handling

frontend/app/recipes/RecipePreview.tsx

@@ -2,6 +2,7 @@
 
 import { useState, useTransition } from 'react';
 import Link from 'next/link';
+import { parseErrorResponse } from '../../lib/error-handler';
 import type {
   Recipe,
   RecipeInventoryPreview,
@@ -74,14 +75,15 @@ export default function RecipePreview({ recipes }: Props) {
         });
 
         if (!res.ok) {
-          const text = await res.text();
-          throw new Error(text || 'Kunde inte hämta recept-preview.');
+          const errorMessage = await parseErrorResponse(res);
+          throw new Error(errorMessage);
         }
 
         const data: RecipeInventoryPreview = await res.json();
         setPreview(data);
       } catch (err) {
-        setError(err instanceof Error ? err.message : 'Okänt fel');
+        const message = err instanceof Error ? err.message : 'Ett okänt fel inträffade.';
+        setError(message);
       }
     });
   };

frontend/app/recipes/[id]/edit/page.tsx

@@ -3,6 +3,7 @@
 import { useState, useEffect } from 'react';
 import { useRouter, useParams } from 'next/navigation';
 import { fetchJson } from '../../../../lib/api';
+import { parseErrorResponse } from '../../../../lib/error-handler';
 import type { Product, Recipe } from '../../../../features/inventory/types';
 
 export default function EditRecipePage() {
@@ -99,12 +100,14 @@ export default function EditRecipePage() {
       });
 
       if (!response.ok) {
-        throw new Error('Kunde inte uppdatera receptet');
+        const errorMessage = await parseErrorResponse(response);
+        throw new Error(errorMessage);
       }
 
       router.push('/recipes');
     } catch (err) {
-      setError((err as Error).message);
+      const message = err instanceof Error ? err.message : 'Ett okänt fel inträffade. Försök igen.';
+      setError(message);
     } finally {
       setIsSaving(false);
     }

frontend/app/recipes/create/CreateRecipePage.tsx

@@ -3,6 +3,7 @@
 import { useState, useEffect } from 'react';
 import { useRouter } from 'next/navigation';
 import { fetchJson } from '../../../lib/api';
+import { parseErrorResponse } from '../../../lib/error-handler';
 import type { Product } from '../../../features/inventory/types';
 
 export default function CreateRecipePage() {
@@ -64,12 +65,14 @@ export default function CreateRecipePage() {
       });
 
       if (!response.ok) {
-        throw new Error('Kunde inte spara receptet');
+        const errorMessage = await parseErrorResponse(response);
+        throw new Error(errorMessage);
       }
 
       router.push('/recipes');
     } catch (err) {
-      setError((err as Error).message);
+      const message = err instanceof Error ? err.message : 'Ett okänt fel inträffade. Försök igen.';
+      setError(message);
     } finally {
       setIsLoading(false);
     }