fix(email): correct signature reminder URL path

Change signature URL in reminder emails from '/sign?doc=' to '/?doc='
to match the correct frontend route.

Updated in:
- ReminderService.sendSingleReminder
- ReminderAsyncService.queueSingleReminder
- Email helper tests

backend/internal/application/services/reminder.go

@@ -142,7 +142,7 @@ func (s *ReminderService) sendSingleReminder(
 		"recipient_name", recipientName,
 		"sent_by", sentBy)
 
-	signURL := fmt.Sprintf("%s/sign?doc=%s", s.baseURL, docID)
+	signURL := fmt.Sprintf("%s/?doc=%s", s.baseURL, docID)
 
 	log := &models.ReminderLog{
 		DocID:          docID,

backend/internal/application/services/reminder_async.go

@@ -139,7 +139,7 @@ func (s *ReminderAsyncService) queueSingleReminder(
 		"recipient_name", recipientName,
 		"sent_by", sentBy)
 
-	signURL := fmt.Sprintf("%s/sign?doc=%s", s.baseURL, docID)
+	signURL := fmt.Sprintf("%s/?doc=%s", s.baseURL, docID)
 
 	// Prepare email data (keys must match template variables)
 	data := map[string]interface{}{

backend/internal/infrastructure/email/helpers_test.go

@@ -146,7 +146,7 @@ func TestSendSignatureReminderEmail(t *testing.T) {
 			locale:          "en",
 			docID:           "doc123",
 			docURL:          "https://example.com/doc.pdf",
-			signURL:         "https://example.com/sign?doc=doc123",
+			signURL:         "https://example.com/?doc=doc123",
 			recipientName:   "John Doe",
 			expectedSubject: "Reminder: Document reading confirmation required",
 			sendError:       nil,
@@ -158,7 +158,7 @@ func TestSendSignatureReminderEmail(t *testing.T) {
 			locale:          "fr",
 			docID:           "doc456",
 			docURL:          "https://exemple.fr/document.pdf",
-			signURL:         "https://exemple.fr/sign?doc=doc456",
+			signURL:         "https://exemple.fr/?doc=doc456",
 			recipientName:   "Marie Dupont",
 			expectedSubject: "Rappel : Confirmation de lecture de document requise",
 			sendError:       nil,