Phase 2: Web dashboard with SSE real-time push

- dashboard.go: SSE hub + HTTP server + price history ring buffer
- static.go: //go:embed for static files
- web/static/index.html: Full dashboard HTML (6 panels)
- web/static/app.js: SSE client, Chart.js price chart, live table updates
- web/static/style.css: GitHub-style dark theme
- main.go: Start dashboard on :8888 + wire price recording + scan results

Dashboard features:
  - Real-time price table (6 coins × 4 exchanges)
  - Arbitrage opportunities table
  - Open positions view
  - Historical trades table (from SQLite)
  - Chart.js price chart with coin/exchange selector
  - Stats summary (total/converged/diverged/flat)
  - 🚫 Zero external Go dependencies (Chart.js loaded from CDN)

main.go

@@ -45,6 +45,10 @@ func main() {
 
 	// Initialize trader
 	trader := NewTrader(cfg, database)
+
+	// Initialize dashboard (web server + SSE)
+	dashboard := NewDashboard(store, trader, database, ":8888")
+	go dashboard.Run()
 	if trader.IsConfigured() {
 		modeLabel := trader.ModeLabel()
 		log.Printf("[Trader] %s mode: automated trading ENABLED (threshold >= %.2f%%, $%.0f/trade)",
@@ -79,6 +83,7 @@ func main() {
 			for {
 				err := runner(func(coin string, price, bid, ask float64) {
 					store.SetWithSpread(coin, name, price, bid, ask)
+					dashboard.RecordPrice(coin, name, price)
 				})
 				log.Printf("[%s] WS error: %v (reconnecting...)", name, err)
 				select {
@@ -155,6 +160,7 @@ func main() {
 
 			// Scan for arbitrage entries using maker fees (limit orders)
 			makerOpps := ScanArbWithFees(store, makerFees)
+			dashboard.UpdateScan(makerOpps)
 			t2 := time.Now()
 
 			for _, opp := range makerOpps {