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/notify/dispatcher.go

@@ -0,0 +1,70 @@
+// Package notify fans out domain events (order paid, order expired,
+// etc.) to every NotificationChannel subscribed to the event. Senders
+// are type-keyed (telegram/webhook/email/...) so adding a new push
+// method means registering one function; no callers change.
+package notify
+
+import (
+	"encoding/json"
+	"sync"
+
+	"github.com/assimon/luuu/model/data"
+	"github.com/assimon/luuu/model/mdb"
+	"github.com/assimon/luuu/util/log"
+)
+
+// Sender delivers an already-rendered text message via a channel row.
+// Config is the channel's Config JSON string (type-specific shape).
+type Sender func(config, text string) error
+
+var (
+	sendersMu sync.RWMutex
+	senders   = map[string]Sender{}
+)
+
+// RegisterSender wires a Sender for a channel type. Called once at
+// package init of each sender file (e.g. telegram_sender.go).
+func RegisterSender(channelType string, s Sender) {
+	sendersMu.Lock()
+	senders[channelType] = s
+	sendersMu.Unlock()
+}
+
+func getSender(channelType string) (Sender, bool) {
+	sendersMu.RLock()
+	defer sendersMu.RUnlock()
+	s, ok := senders[channelType]
+	return s, ok
+}
+
+// Dispatch delivers text to every enabled channel subscribed to event.
+// Per-channel failures are logged but don't abort the fan-out — one
+// broken TG token shouldn't prevent webhook delivery.
+func Dispatch(event, text string) {
+	channels, err := data.ListEnabledChannelsByEvent(event)
+	if err != nil {
+		log.Sugar.Errorf("[notify] list channels failed: %v", err)
+		return
+	}
+	for _, ch := range channels {
+		sender, ok := getSender(ch.Type)
+		if !ok {
+			log.Sugar.Warnf("[notify] no sender registered for type=%s (channel_id=%d)", ch.Type, ch.ID)
+			continue
+		}
+		go func(c mdb.NotificationChannel) {
+			if err := sender(c.Config, text); err != nil {
+				log.Sugar.Errorf("[notify] send failed type=%s channel_id=%d: %v", c.Type, c.ID, err)
+			}
+		}(ch)
+	}
+}
+
+// ParseConfig helper for senders: unmarshal channel Config JSON into
+// an arbitrary struct, returning a typed error on invalid JSON.
+func ParseConfig(raw string, out interface{}) error {
+	if raw == "" {
+		return ErrEmptyConfig
+	}
+	return json.Unmarshal([]byte(raw), out)
+}