feat(17-02): implement scheduler package with gocron wrapper and job lifecycle

- Scheduler wraps gocron with Start/Stop lifecycle
- Start loads enabled jobs from DB and registers cron schedules
- AddJob/RemoveJob persist to DB and sync with gocron
- RunJob for manual trigger with OnComplete callback
- JobResult struct for notification bridge
- Promote gocron/v2 v2.19.1 to direct dependency

pkg/scheduler/jobs.go

@@ -1 +1,21 @@
 package scheduler
+
+import "time"
+
+// Job represents a scheduled scan job with its runtime function.
+type Job struct {
+	Name           string
+	CronExpr       string
+	ScanCommand    string
+	NotifyTelegram bool
+	Enabled        bool
+	RunFunc        func(ctx interface{}) (int, error)
+}
+
+// JobResult contains the outcome of a scheduled or manually triggered scan job.
+type JobResult struct {
+	JobName      string
+	FindingCount int
+	Duration     time.Duration
+	Error        error
+}