feat(storage): paginate operations history with prev/next controls

Backend:
- ListStorageJobs(limit, offset) adds OFFSET for pagination
- CountStorageJobs() returns total row count for UI
- handler returns { jobs, total, limit, offset }
- JobManager.List(limit, offset) updated signature

Frontend:
- loadJobs(offset) with default 0
- Pagination UI: 'Mostrando X-Y de Z' + Anterior/Siguiente buttons
- After job start/end, reloads from offset 0
- listStorageJobs(limit, offset) API updated

Tests: fix List/ListStorageJobs calls to include offset=0

internal/db/queries_storage.go

@@ -159,13 +159,13 @@ func (d *DB) TrimJobOutput(id int64, maxLines int) error {
 	return nil
 }
 
-func (d *DB) ListStorageJobs(limit int) ([]StorageJob, error) {
+func (d *DB) ListStorageJobs(limit, offset int) ([]StorageJob, error) {
 	if limit <= 0 {
-		limit = 50
+		limit = 20
 	}
 	rows, err := d.conn.Query(`
 		SELECT id, kind, status, args_json, pid, started_at, finished_at, exit_code, output, error, created_at
-		FROM storage_jobs ORDER BY created_at DESC LIMIT ?`, limit)
+		FROM storage_jobs ORDER BY created_at DESC LIMIT ? OFFSET ?`, limit, offset)
 	if err != nil {
 		return nil, fmt.Errorf("list storage jobs: %w", err)
 	}
@@ -182,6 +182,15 @@ func (d *DB) ListStorageJobs(limit int) ([]StorageJob, error) {
 	return jobs, rows.Err()
 }
 
+func (d *DB) CountStorageJobs() (int, error) {
+	var count int
+	err := d.conn.QueryRow(`SELECT COUNT(1) FROM storage_jobs`).Scan(&count)
+	if err != nil {
+		return 0, fmt.Errorf("count storage jobs: %w", err)
+	}
+	return count, nil
+}
+
 func (d *DB) GetRunningJob() (*StorageJob, error) {
 	row := d.conn.QueryRow(`
 		SELECT id, kind, status, args_json, pid, started_at, finished_at, exit_code, output, error, created_at