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/config/settings_bridge.go

@@ -0,0 +1,34 @@
+package config
+
+// Settings lookups are injected at runtime by bootstrap (after DB init)
+// to keep the config package free of a `model/data` import, which would
+// create a cycle via `model/dao -> config`.
+//
+// If unset (e.g. during early startup or tests) the getters return the
+// zero string / 0 and callers fall through to the .env / default path.
+
+// SettingsGetString is installed by bootstrap.Init with a closure that
+// reads from the settings table. Runtime-only.
+var SettingsGetString func(key string) string
+
+func settingsRateApiUrl() string {
+	if SettingsGetString == nil {
+		return ""
+	}
+	return SettingsGetString("rate.api_url")
+}
+
+func settingsForcedUsdtRate() float64 {
+	if SettingsGetString == nil {
+		return 0
+	}
+	raw := SettingsGetString("rate.forced_usdt_rate")
+	if raw == "" {
+		return 0
+	}
+	f, err := parseFloat(raw)
+	if err != nil {
+		return 0
+	}
+	return f
+}