fix: add total_debit/total_credit aggregations to journal entries list

The findAll query was missing SUM aggregations, so the frontend received
no total_debit/total_credit fields and fell back to displaying $0.00.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/modules/journal-entries/journal-entries.service.ts

@@ -13,6 +13,8 @@ export class JournalEntriesService {
   async findAll(filters: { from?: string; to?: string; accountId?: string; type?: string }) {
     let sql = `
       SELECT je.*,
+        COALESCE(SUM(jel.debit), 0) as total_debit,
+        COALESCE(SUM(jel.credit), 0) as total_credit,
         json_agg(json_build_object(
           'id', jel.id, 'account_id', jel.account_id,
           'debit', jel.debit, 'credit', jel.credit, 'memo', jel.memo,