Add processing fee option to PDF export modal

- Add checkbox to include 5% processing fee in PDF exports
- Install PDF generation dependencies (@pdfme/common, @pdfme/generator, sharp)
- Add server-side expenses API endpoints
- Update PDF options interface to support processing fee toggle

components/PDFOptionsModal.vue

@@ -91,6 +91,18 @@
                 <div class="text-sm text-gray-500">Show establishment name, date, description</div>
               </div>
             </label>
+
+            <label class="flex items-center gap-3 cursor-pointer">
+              <input
+                v-model="options.includeProcessingFee"
+                type="checkbox"
+                class="checkbox checkbox-primary"
+              />
+              <div>
+                <div class="font-medium">Include Processing Fee</div>
+                <div class="text-sm text-gray-500">Add 5% processing fee to totals</div>
+              </div>
+            </label>
           </div>
         </div>
 
@@ -174,6 +186,7 @@ interface PDFOptions {
   includeReceipts: boolean;
   includeSummary: boolean;
   includeDetails: boolean;
+  includeProcessingFee: boolean;
   pageFormat: 'A4' | 'Letter' | 'Legal';
 }
 
@@ -187,6 +200,7 @@ const options = ref<PDFOptions>({
   includeReceipts: true,
   includeSummary: true,
   includeDetails: true,
+  includeProcessingFee: true,
   pageFormat: 'A4'
 });