Add automated backup system with SQLite VACUUM

- Implement backup package with SQLite VACUUM INTO for safe backups
- Add scheduler with configurable interval (default: 24h)
- Add retention policy with automatic cleanup (default: 7 days)
- Add optional gzip compression (~10x size reduction)
- Add comprehensive tests for backup creation and cleanup
- Integrate backup scheduler in main.go with graceful shutdown
- Add backup configuration variables (BACKUP_ENABLED, BACKUP_INTERVAL, BACKUP_RETENTION_DAYS, BACKUP_PATH, BACKUP_COMPRESS)
- Backups run automatically in background goroutine
- Coverage: backup package 52.7%

internal/infrastructure/backup/scheduler.go

@@ -0,0 +1,77 @@
+package backup
+
+import (
+	"database/sql"
+	"time"
+
+	"apocapoc-api/internal/infrastructure/logger"
+)
+
+type Scheduler struct {
+	db     *sql.DB
+	config Config
+	stopCh chan struct{}
+}
+
+func NewScheduler(db *sql.DB, config Config) *Scheduler {
+	return &Scheduler{
+		db:     db,
+		config: config,
+		stopCh: make(chan struct{}),
+	}
+}
+
+func (s *Scheduler) Start() {
+	if !s.config.Enabled {
+		logger.Info().Msg("Backup scheduler is disabled")
+		return
+	}
+
+	logger.Info().
+		Dur("interval", s.config.Interval).
+		Int("retention_days", s.config.RetentionDays).
+		Str("path", s.config.Path).
+		Bool("compress", s.config.Compress).
+		Msg("Starting backup scheduler")
+
+	go s.run()
+}
+
+func (s *Scheduler) run() {
+	if err := CreateBackup(s.db, s.config); err != nil {
+		logger.Error().Err(err).Msg("Initial backup failed")
+	}
+
+	if err := CleanOldBackups(s.config); err != nil {
+		logger.Error().Err(err).Msg("Initial cleanup failed")
+	}
+
+	ticker := time.NewTicker(s.config.Interval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			logger.Debug().Msg("Running scheduled backup")
+
+			if err := CreateBackup(s.db, s.config); err != nil {
+				logger.Error().Err(err).Msg("Scheduled backup failed")
+				continue
+			}
+
+			if err := CleanOldBackups(s.config); err != nil {
+				logger.Error().Err(err).Msg("Backup cleanup failed")
+			}
+
+		case <-s.stopCh:
+			logger.Info().Msg("Backup scheduler stopped")
+			return
+		}
+	}
+}
+
+func (s *Scheduler) Stop() {
+	if s.config.Enabled {
+		close(s.stopCh)
+	}
+}