Migrate Backup Logic to Core Layer

[baync180705]

Move the existing backup business logic from the legacy system/backup package to the new internal/core/backup directory to align with the new architecture.

Requirements:

• Move Files: Move all system/backup/*.go files to internal/core/backup/.
• Update Package: Change the package declaration in moved files to package backup.
• Fix Imports: Update internal imports to point to new locations (e.g., internal/platform, internal/domain).
• Test: Ensure that the program runs as expected and does not crash.