refactor(cron): migrate cron jobs to foundation scheduler

Replace custom goroutine-based scheduling in cron jobs with centralized
foundation scheduler. Each cron job now exposes a RunOnce method called
by the scheduler instead of managing its own ticker loop.

Changes:
- Remove interval/enabled config from cron job structs
- Convert Start() methods to RunOnce() for all cron jobs
- Add scheduler setup in main.go with configurable intervals
- Update foundation dependency to v0.6.0 for scheduler support
- Update tests to validate RunOnce nil-safety

internal/cron/log_cleaner.go

@@ -25,48 +25,27 @@ type LogCleaner struct {
 	rdb           *redis.Client
 	retentionDays int
 	maxRecords    int64
-	interval      time.Duration
 	partitioner   *service.LogPartitioner
 }
 
-func NewLogCleaner(db *gorm.DB, rdb *redis.Client, retentionDays int, maxRecords int64, interval time.Duration, partitioner *service.LogPartitioner) *LogCleaner {
-	if interval <= 0 {
-		interval = time.Hour
-	}
+func NewLogCleaner(db *gorm.DB, rdb *redis.Client, retentionDays int, maxRecords int64, partitioner *service.LogPartitioner) *LogCleaner {
 	return &LogCleaner{
 		db:            db,
 		rdb:           rdb,
 		retentionDays: retentionDays,
 		maxRecords:    maxRecords,
-		interval:      interval,
 		partitioner:   partitioner,
 	}
 }
 
-func (c *LogCleaner) Start(ctx context.Context) {
+// RunOnce executes a single log cleanup. Called by scheduler.
+func (c *LogCleaner) RunOnce(ctx context.Context) {
 	if c == nil || c.db == nil {
 		return
 	}
-	if ctx == nil {
-		ctx = context.Background()
-	}
-
 	if err := c.cleanOnce(ctx); err != nil {
 		slog.Default().Warn("log cleaner run failed", "err", err)
 	}
-
-	ticker := time.NewTicker(c.interval)
-	defer ticker.Stop()
-	for {
-		select {
-		case <-ctx.Done():
-			return
-		case <-ticker.C:
-			if err := c.cleanOnce(ctx); err != nil {
-				slog.Default().Warn("log cleaner run failed", "err", err)
-			}
-		}
-	}
 }
 
 func (c *LogCleaner) cleanOnce(ctx context.Context) error {