feat: enhance receipt import to support PDF files with updated UI and backend processing

frontend/app/kvitto/ReceiptImportClient.tsx

@@ -29,7 +29,11 @@ export default function ReceiptImportClient() {
     const file = e.target.files?.[0];
     if (!file) return;
     setSelectedFile(file);
-    setPreview(URL.createObjectURL(file));
+    if (file.type === 'application/pdf') {
+      setPreview('pdf');
+    } else {
+      setPreview(URL.createObjectURL(file));
+    }
     setRows([]);
     setError(null);
     setSavedCount(null);
@@ -119,12 +123,18 @@ export default function ReceiptImportClient() {
         <input
           ref={fileRef}
           type="file"
-          accept="image/*"
+          accept="image/*,application/pdf"
           capture="environment"
           onChange={handleFileChange}
           style={{ display: 'none' }}
         />
-        {preview ? (
+        {preview === 'pdf' ? (
+          <div style={{ padding: '1rem', color: '#333' }}>
+            <div style={{ fontSize: '2.5rem', marginBottom: '0.5rem' }}>📄</div>
+            <div style={{ fontWeight: 600 }}>{selectedFile?.name}</div>
+            <div style={{ fontSize: '0.85rem', color: '#888', marginTop: '0.25rem' }}>PDF-kvitto valt</div>
+          </div>
+        ) : preview ? (
           // eslint-disable-next-line @next/next/no-img-element
           <img
             src={preview}
@@ -136,7 +146,7 @@ export default function ReceiptImportClient() {
             <div style={{ fontSize: '2.5rem', marginBottom: '0.5rem' }}>📷</div>
             <div style={{ fontWeight: 600 }}>Fotografera eller välj kvitto</div>
             <div style={{ fontSize: '0.85rem', marginTop: '0.25rem' }}>
-              Klicka för att välja bild (JPEG, PNG, WebP)
+              Klicka för att välja bild (JPEG, PNG, WebP) eller PDF
             </div>
           </div>
         )}