Add /config trial VPN generation for users (1 day default)

Users get Remnawave subscription via /config or inline button; TRIAL_USER_DAYS and panel lookup by Telegram ID.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/db/users.go

@@ -46,6 +46,30 @@ func (d *DB) SaveVPNUser(ctx context.Context, u VPNUser) error {
 	return err
 }
 
+func (d *DB) GetVPNByTelegramID(ctx context.Context, telegramID int64) (*VPNUser, error) {
+	row := d.pool.QueryRow(ctx, `
+		SELECT id, telegram_id, remnawave_uuid::text, remnawave_username,
+			external_squad_uuid::text, internal_squad_uuids::text[], expire_at
+		FROM vpn_users
+		WHERE telegram_id = $1
+		ORDER BY expire_at DESC NULLS LAST
+		LIMIT 1`, telegramID)
+
+	var u VPNUser
+	var ext *string
+	var internal []string
+	err := row.Scan(&u.ID, &u.TelegramID, &u.RemnawaveUUID, &u.RemnawaveUsername, &ext, &internal, &u.ExpireAt)
+	if err == pgx.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	u.ExternalSquadUUID = ext
+	u.InternalSquadUUIDs = internal
+	return &u, nil
+}
+
 func (d *DB) GetVPNByUsername(ctx context.Context, username string) (*VPNUser, error) {
 	row := d.pool.QueryRow(ctx, `
 		SELECT id, telegram_id, remnawave_uuid::text, remnawave_username,