feat(yedek): JSON tam hane yedeği backend (önizleme, geri yükleme, geri dönüş noktaları)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/src/services/mod.rs

@@ -2,6 +2,7 @@
 
 pub mod account;
 pub mod asset;
+pub mod backup;
 pub mod bank_import;
 pub mod budget;
 pub mod calendar;