feat: add admin panel with multi-chain support and notification system

- Add full admin REST API: auth, API keys, chains, chain tokens, wallets,
  orders, RPC nodes, settings, dashboard stats, notifications
- Add JWT-based admin authentication and API key auth middleware
- Add multi-chain listeners: BSC, ETH, Polygon, Plasma, EVM WebSocket
- Add RPC node health check job with automatic failover
- Add Telegram notification channel for order events
- Add installer for first-run database initialization
- Add new DB models: admin_user, api_key, chain, chain_token,
  rpc_node, settings, notification_channel
- Add order statistics aggregation (daily/monthly/by-chain)
- Serve built admin SPA from embedded www/ assets
- Add comprehensive test coverage for all new features

src/model/data/notification_channel_data.go

@@ -0,0 +1,81 @@
+package data
+
+import (
+	"encoding/json"
+	"strings"
+
+	"github.com/assimon/luuu/model/dao"
+	"github.com/assimon/luuu/model/mdb"
+)
+
+// ListNotificationChannels returns all rows, optionally filtered by type.
+func ListNotificationChannels(channelType string) ([]mdb.NotificationChannel, error) {
+	var rows []mdb.NotificationChannel
+	tx := dao.Mdb.Model(&mdb.NotificationChannel{})
+	if channelType != "" {
+		tx = tx.Where("type = ?", strings.ToLower(channelType))
+	}
+	err := tx.Order("id DESC").Find(&rows).Error
+	return rows, err
+}
+
+// ListEnabledChannelsByEvent returns enabled rows whose Events JSON has
+// the named event key set to true. Done in Go (rather than JSON_EXTRACT)
+// because the runtime DB is DB-agnostic (MySQL/Postgres/SQLite).
+func ListEnabledChannelsByEvent(event string) ([]mdb.NotificationChannel, error) {
+	var rows []mdb.NotificationChannel
+	if err := dao.Mdb.Model(&mdb.NotificationChannel{}).
+		Where("enabled = ?", true).
+		Find(&rows).Error; err != nil {
+		return nil, err
+	}
+	out := rows[:0]
+	for _, r := range rows {
+		events := map[string]bool{}
+		if r.Events != "" {
+			_ = json.Unmarshal([]byte(r.Events), &events)
+		}
+		if events[event] {
+			out = append(out, r)
+		}
+	}
+	return out, nil
+}
+
+// GetFirstEnabledTelegramChannel returns the oldest enabled telegram
+// row, or nil ID if none. Telegram bot startup uses this as the primary
+// instance backing /start and command handlers.
+func GetFirstEnabledTelegramChannel() (*mdb.NotificationChannel, error) {
+	row := new(mdb.NotificationChannel)
+	err := dao.Mdb.Model(row).
+		Where("type = ?", mdb.NotificationTypeTelegram).
+		Where("enabled = ?", true).
+		Order("id ASC").
+		Limit(1).Find(row).Error
+	return row, err
+}
+
+// GetNotificationChannelByID fetches by PK.
+func GetNotificationChannelByID(id uint64) (*mdb.NotificationChannel, error) {
+	row := new(mdb.NotificationChannel)
+	err := dao.Mdb.Model(row).Limit(1).Find(row, id).Error
+	return row, err
+}
+
+// CreateNotificationChannel inserts a new row.
+func CreateNotificationChannel(row *mdb.NotificationChannel) error {
+	return dao.Mdb.Create(row).Error
+}
+
+// UpdateNotificationChannelFields patches mutable columns.
+func UpdateNotificationChannelFields(id uint64, fields map[string]interface{}) error {
+	if len(fields) == 0 {
+		return nil
+	}
+	return dao.Mdb.Model(&mdb.NotificationChannel{}).Where("id = ?", id).Updates(fields).Error
+}
+
+// DeleteNotificationChannelByID soft-deletes a row.
+func DeleteNotificationChannelByID(id uint64) error {
+	return dao.Mdb.Where("id = ?", id).Delete(&mdb.NotificationChannel{}).Error
+}