feat: real trading mode, auto-stop after 5 trades, HL testnet support

- config.json: test_mode=false, ready for sim/testnet trading
- trader.go: auto-stop after 5 real trades, exchange response logging,
  Stop()/Start() API, shuttingDown flag for graceful stop
- dashboard.go: POST /api/stop + POST /api/start endpoints,
  trading status in SSE stats
- exchange/hyperliquid.go: switch HL WS to testnet endpoint
- exchange/hyperliquid_trade.go: switch REST to testnet endpoint,
  support base64 + 32-byte EVM private keys
- main.go: listen on trader.StopCh (graceful, no process exit)
- scanner.go: trim TrackedCoins to only 6 core coins (DOGE/LINK/ONDO/OP/WIF/ARB)
- .gitignore: ignore main binary

dashboard.go

@@ -240,6 +240,8 @@ func (d *Dashboard) Run() {
 	mux.HandleFunc("GET /api/trade/", d.handleTradeDetail)
 	mux.HandleFunc("GET /api/connections", d.handleConnStatus) // P3-5
 	mux.HandleFunc("GET /events", d.handleSSE)
+	mux.HandleFunc("POST /api/stop", d.handleStop)
+	mux.HandleFunc("POST /api/start", d.handleStart)
 
 	server := &http.Server{
 		Addr:         d.addr,
@@ -479,6 +481,15 @@ func (d *Dashboard) broadcastLoop() {
 		d.connMu.RUnlock()
 		stats["connections"] = connInfo
 
+		// Trading status
+		stats["trading"] = map[string]interface{}{
+			"active":   !d.trader.IsShuttingDown(),
+			"mode":     d.trader.ModeLabel(),
+			"test":     d.trader.cfg.TestMode,
+			"target":   d.trader.realTradesTarget,
+			"done":     d.trader.realTradesDone,
+		}
+
 		// Per-exchange fund tracking
 		exFunds := d.trader.GetExchangeFunds()
 		exFundsMap := make(map[string]map[string]float64, len(exFunds))
@@ -708,6 +719,16 @@ func (d *Dashboard) handleSSE(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func (d *Dashboard) handleStop(w http.ResponseWriter, r *http.Request) {
+	d.trader.Stop()
+	writeJSON(w, map[string]string{"status": "stopped", "message": "Trading stopped, positions closing"})
+}
+
+func (d *Dashboard) handleStart(w http.ResponseWriter, r *http.Request) {
+	d.trader.Start()
+	writeJSON(w, map[string]string{"status": "started", "message": "Trading resumed"})
+}
+
 func writeJSON(w http.ResponseWriter, v interface{}) {
 	w.Header().Set("Content-Type", "application/json")
 	json.NewEncoder(w).Encode(v)