feat(17-02): add gocron dependency, subscribers and scheduled_jobs tables with CRUD

- Add gocron/v2 v2.19.1 as direct dependency
- Append subscribers and scheduled_jobs CREATE TABLE to schema.sql
- Implement full subscriber CRUD (Add/Remove/List/IsSubscribed)
- Implement full scheduled job CRUD (Save/List/Get/Delete/UpdateLastRun/SetEnabled)

pkg/storage/scheduled_jobs.go

@@ -0,0 +1,111 @@
+package storage
+
+import (
+	"database/sql"
+	"time"
+)
+
+// ScheduledJob represents a cron-based scheduled scan job.
+type ScheduledJob struct {
+	ID              int64
+	Name            string
+	CronExpr        string
+	ScanCommand     string
+	NotifyTelegram  bool
+	Enabled         bool
+	LastRun         *time.Time
+	NextRun         *time.Time
+	CreatedAt       time.Time
+}
+
+// SaveScheduledJob inserts a new scheduled job. Returns the new row ID.
+func (db *DB) SaveScheduledJob(j ScheduledJob) (int64, error) {
+	res, err := db.sql.Exec(
+		`INSERT INTO scheduled_jobs (name, cron_expr, scan_command, notify_telegram, enabled)
+		 VALUES (?, ?, ?, ?, ?)`,
+		j.Name, j.CronExpr, j.ScanCommand, j.NotifyTelegram, j.Enabled,
+	)
+	if err != nil {
+		return 0, err
+	}
+	return res.LastInsertId()
+}
+
+// ListScheduledJobs returns all scheduled jobs.
+func (db *DB) ListScheduledJobs() ([]ScheduledJob, error) {
+	rows, err := db.sql.Query(
+		`SELECT id, name, cron_expr, scan_command, notify_telegram, enabled, last_run, next_run, created_at
+		 FROM scheduled_jobs ORDER BY id`,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var jobs []ScheduledJob
+	for rows.Next() {
+		var j ScheduledJob
+		var lastRun, nextRun sql.NullTime
+		if err := rows.Scan(&j.ID, &j.Name, &j.CronExpr, &j.ScanCommand,
+			&j.NotifyTelegram, &j.Enabled, &lastRun, &nextRun, &j.CreatedAt); err != nil {
+			return nil, err
+		}
+		if lastRun.Valid {
+			j.LastRun = &lastRun.Time
+		}
+		if nextRun.Valid {
+			j.NextRun = &nextRun.Time
+		}
+		jobs = append(jobs, j)
+	}
+	return jobs, rows.Err()
+}
+
+// GetScheduledJob returns a single scheduled job by name.
+func (db *DB) GetScheduledJob(name string) (*ScheduledJob, error) {
+	var j ScheduledJob
+	var lastRun, nextRun sql.NullTime
+	err := db.sql.QueryRow(
+		`SELECT id, name, cron_expr, scan_command, notify_telegram, enabled, last_run, next_run, created_at
+		 FROM scheduled_jobs WHERE name = ?`, name,
+	).Scan(&j.ID, &j.Name, &j.CronExpr, &j.ScanCommand,
+		&j.NotifyTelegram, &j.Enabled, &lastRun, &nextRun, &j.CreatedAt)
+	if err != nil {
+		return nil, err
+	}
+	if lastRun.Valid {
+		j.LastRun = &lastRun.Time
+	}
+	if nextRun.Valid {
+		j.NextRun = &nextRun.Time
+	}
+	return &j, nil
+}
+
+// DeleteScheduledJob removes a scheduled job by name. Returns rows affected.
+func (db *DB) DeleteScheduledJob(name string) (int64, error) {
+	res, err := db.sql.Exec(`DELETE FROM scheduled_jobs WHERE name = ?`, name)
+	if err != nil {
+		return 0, err
+	}
+	return res.RowsAffected()
+}
+
+// UpdateJobLastRun updates the last_run and next_run timestamps for a job.
+func (db *DB) UpdateJobLastRun(name string, lastRun time.Time, nextRun *time.Time) error {
+	var nr sql.NullTime
+	if nextRun != nil {
+		nr = sql.NullTime{Time: *nextRun, Valid: true}
+	}
+	_, err := db.sql.Exec(
+		`UPDATE scheduled_jobs SET last_run = ?, next_run = ? WHERE name = ?`,
+		lastRun, nr, name,
+	)
+	return err
+}
+
+// SetJobEnabled updates the enabled flag for a scheduled job.
+func (db *DB) SetJobEnabled(name string, enabled bool) error {
+	_, err := db.sql.Exec(`UPDATE scheduled_jobs SET enabled = ? WHERE name = ?`, enabled, name)
+	return err
+}