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/mdb/chain_token.go

@@ -0,0 +1,24 @@
+package mdb
+
+const (
+	ChainTokenStatusEnable  = 1
+	ChainTokenStatusDisable = 2
+)
+
+// ChainToken describes a token to watch on a given chain. Replaces the
+// hardcoded USDT/USDC contract addresses in task/listen_eth.go. Scanners
+// load this table on startup (and refresh periodically) to learn which
+// contracts to subscribe to.
+type ChainToken struct {
+	Network         string  `gorm:"column:network;size:32;uniqueIndex:chain_tokens_network_symbol_uindex,priority:1" json:"network" example:"tron"`
+	Symbol          string  `gorm:"column:symbol;size:32;uniqueIndex:chain_tokens_network_symbol_uindex,priority:2" json:"symbol" example:"USDT"`
+	ContractAddress string  `gorm:"column:contract_address;size:128" json:"contract_address" example:"TR7NHqjeKQxGTCi8q8ZY4pL8otSzgjLj6t"`
+	Decimals        int     `gorm:"column:decimals;default:6" json:"decimals" example:"6"`
+	Enabled         bool    `gorm:"column:enabled;default:true" json:"enabled" example:"true"`
+	MinAmount       float64 `gorm:"column:min_amount;default:0" json:"min_amount" example:"1.0"`
+	BaseModel
+}
+
+func (c *ChainToken) TableName() string {
+	return "chain_tokens"
+}