export: use filename from Content-Disposition header in browser

Fix issue where frontend was ignoring server's Content-Disposition
header and using only config name + '.csv' for exported files.

Added getFilenameFromResponse() helper to extract proper filename
from Content-Disposition header and use it for downloaded files.

Applied to both:
- exportCSV() function
- exportCSVWithCustomPrice() function

Now files are downloaded with correct format:
  YYYY-MM-DD (PROJECT-NAME) BOM.csv

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

web/templates/index.html

@@ -1716,6 +1716,14 @@ async function saveConfig(showNotification = true) {
     }
 }
 
+// Helper function to extract filename from Content-Disposition header
+function getFilenameFromResponse(resp) {
+    const contentDisposition = resp.headers.get('content-disposition');
+    if (!contentDisposition) return null;
+    const matches = contentDisposition.match(/filename="?([^"]+)"?/);
+    return matches && matches[1] ? matches[1] : null;
+}
+
 async function exportCSV() {
     if (cart.length === 0) return;
 
@@ -1740,7 +1748,7 @@ async function exportCSV() {
         const url = window.URL.createObjectURL(blob);
         const a = document.createElement('a');
         a.href = url;
-        a.download = (configName || 'config') + '.csv';
+        a.download = getFilenameFromResponse(resp) || (configName || 'config') + '.csv';
         a.click();
         window.URL.revokeObjectURL(url);
     } catch(e) {
@@ -1993,7 +2001,7 @@ async function exportCSVWithCustomPrice() {
         const url = window.URL.createObjectURL(blob);
         const a = document.createElement('a');
         a.href = url;
-        a.download = (configName || 'config') + '.csv';
+        a.download = getFilenameFromResponse(resp) || (configName || 'config') + '.csv';
         a.click();
         window.URL.revokeObjectURL(url);
     } catch(e) {