fix(backup): detect modified files using SHA-256 checksums

[olxgdm]

Fix backup synchronization logic to detect modified tracked files instead of checking only for backup file existence.

Previously, the backup command skipped files whenever a stored backup already existed, even if the original file had been modified after the initial backup.

This change introduces SHA-256 checksum comparison between the original file and the stored backup to determine whether the backup is up to date.

Changes

• Replaced backup existence check with checksum-based validation
• Added SHA-256 file hashing using OpenSSL (EVP_* API)
• Added StoredBackupIsUpToDate() logic
• Updated backup flow to re-backup modified files
• Added OpenSSL crypto linkage in CMake

Result

Backup execution now:

• skips files only when contents are identical
• correctly detects modified tracked files
• creates updated backups when file contents change

Technical Notes

• SHA-256 hashes are calculated incrementally using buffered file reads
• OpenSSL Crypto component is linked via OpenSSL::Crypto

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
82.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud