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/chain_data.go

@@ -0,0 +1,54 @@
+package data
+
+import (
+	"strings"
+
+	"github.com/assimon/luuu/model/dao"
+	"github.com/assimon/luuu/model/mdb"
+)
+
+// ListChains returns all chain rows ordered by id.
+func ListChains() ([]mdb.Chain, error) {
+	var rows []mdb.Chain
+	err := dao.Mdb.Model(&mdb.Chain{}).Order("id ASC").Find(&rows).Error
+	return rows, err
+}
+
+// ListEnabledChains returns only rows with Enabled=true.
+func ListEnabledChains() ([]mdb.Chain, error) {
+	var rows []mdb.Chain
+	err := dao.Mdb.Model(&mdb.Chain{}).
+		Where("enabled = ?", true).
+		Order("id ASC").Find(&rows).Error
+	return rows, err
+}
+
+// GetChainByNetwork fetches one row by network key.
+func GetChainByNetwork(network string) (*mdb.Chain, error) {
+	row := new(mdb.Chain)
+	err := dao.Mdb.Model(row).
+		Where("network = ?", strings.ToLower(strings.TrimSpace(network))).
+		Limit(1).Find(row).Error
+	return row, err
+}
+
+// IsChainEnabled returns whether the row exists and Enabled=true. A
+// missing row is treated as disabled — scanners must be able to
+// short-circuit even before the admin creates the chain entry.
+func IsChainEnabled(network string) bool {
+	row, err := GetChainByNetwork(network)
+	if err != nil || row.ID == 0 {
+		return false
+	}
+	return row.Enabled
+}
+
+// UpdateChainFields patches mutable columns.
+func UpdateChainFields(network string, fields map[string]interface{}) error {
+	if len(fields) == 0 {
+		return nil
+	}
+	return dao.Mdb.Model(&mdb.Chain{}).
+		Where("network = ?", strings.ToLower(strings.TrimSpace(network))).
+		Updates(fields).Error
+}