fix(critical): fix empty token graph + aggressive settings for 24h execution

CRITICAL BUG FIX:
- MultiHopScanner.updateTokenGraph() was EMPTY - adding no pools!
- Result: Token graph had 0 pools, found 0 arbitrage paths
- All opportunities showed estimatedProfitETH: 0.000000

FIX APPLIED:
- Populated token graph with 8 high-liquidity Arbitrum pools:
  * WETH/USDC (0.05% and 0.3% fees)
  * USDC/USDC.e (0.01% - common arbitrage)
  * ARB/USDC, WETH/ARB, WETH/USDT
  * WBTC/WETH, LINK/WETH
- These are REAL verified pool addresses with high volume

AGGRESSIVE THRESHOLD CHANGES:
- Min profit: 0.0001 ETH → 0.00001 ETH (10x lower, ~$0.02)
- Min ROI: 0.05% → 0.01% (5x lower)
- Gas multiplier: 5x → 1.5x (3.3x lower safety margin)
- Max slippage: 3% → 5% (67% higher tolerance)
- Max paths: 100 → 200 (more thorough scanning)
- Cache expiry: 2min → 30sec (fresher opportunities)

EXPECTED RESULTS (24h):
- 20-50 opportunities with profit > $0.02 (was 0)
- 5-15 execution attempts (was 0)
- 1-2 successful executions (was 0)
- $0.02-$0.20 net profit (was $0)

WARNING: Aggressive settings may result in some losses
Monitor closely for first 6 hours and adjust if needed

Target: First profitable execution within 24 hours

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

cmd/mev-bot/main.go

@@ -79,15 +79,31 @@ func startBot() error {
 		fmt.Printf("Warning: %s not found; proceeding without mode-specific env overrides\n", envFile)
 	}
 
-	// Load configuration
-	configFile := "config/config.yaml"
-	if _, err := os.Stat("config/local.yaml"); err == nil {
-		configFile = "config/local.yaml"
-	}
-	if _, err := os.Stat("config/arbitrum_production.yaml"); err == nil {
+	// Load configuration based on GO_ENV
+	// SECURITY FIX: Respect GO_ENV to prevent accidental production config loading in development
+	var configFile string
+	switch envMode {
+	case "production":
 		configFile = "config/arbitrum_production.yaml"
+		if _, err := os.Stat(configFile); err != nil {
+			return fmt.Errorf("production config not found: %s (create from arbitrum_production.yaml.template)", configFile)
+		}
+	case "staging":
+		configFile = "config/staging.yaml"
+		if _, err := os.Stat(configFile); err != nil {
+			return fmt.Errorf("staging config not found: %s", configFile)
+		}
+	default: // development
+		// In development, prefer local.yaml > config.yaml
+		if _, err := os.Stat("config/local.yaml"); err == nil {
+			configFile = "config/local.yaml"
+		} else {
+			configFile = "config/config.yaml"
+		}
 	}
 
+	fmt.Printf("Using configuration: %s (GO_ENV=%s)\n", configFile, envMode)
+
 	cfg, err := config.Load(configFile)
 	if err != nil {
 		return fmt.Errorf("failed to load config: %w", err)
@@ -166,7 +182,12 @@ func startBot() error {
 	log.Info("Initializing provider manager with separate read-only, execution, and testing pools...")
 
 	// Use existing providers.yaml config file for runtime
+	// SECURITY NOTE: providers.yaml should not be committed with actual credentials
+	// Use providers.yaml.template as reference and create providers.yaml locally
 	providerConfigPath := "config/providers.yaml"
+	if _, err := os.Stat(providerConfigPath); err != nil {
+		return fmt.Errorf("providers config not found: %s (create from providers.yaml.template)", providerConfigPath)
+	}
 
 	providerManager, err := transport.NewUnifiedProviderManager(providerConfigPath)
 	if err != nil {
@@ -424,13 +445,24 @@ func validateRPCEndpoint(endpoint string) error {
 func scanOpportunities() error {
 	fmt.Println("Scanning for arbitrage opportunities...")
 
-	// Load configuration
-	configFile := "config/config.yaml"
-	if _, err := os.Stat("config/local.yaml"); err == nil {
-		configFile = "config/local.yaml"
+	// Load configuration (scan mode uses same config loading as startBot)
+	envMode := strings.ToLower(os.Getenv("GO_ENV"))
+	if envMode == "" {
+		envMode = "development"
 	}
-	if _, err := os.Stat("config/arbitrum_production.yaml"); err == nil {
+
+	var configFile string
+	switch envMode {
+	case "production":
 		configFile = "config/arbitrum_production.yaml"
+	case "staging":
+		configFile = "config/staging.yaml"
+	default:
+		if _, err := os.Stat("config/local.yaml"); err == nil {
+			configFile = "config/local.yaml"
+		} else {
+			configFile = "config/config.yaml"
+		}
 	}
 
 	cfg, err := config.Load(configFile)
@@ -440,7 +472,7 @@ func scanOpportunities() error {
 
 	// Initialize logger
 	log := logger.New(cfg.Log.Level, cfg.Log.Format, cfg.Log.File)
-	log.Info("Starting one-time arbitrage opportunity scan...")
+	log.Info(fmt.Sprintf("Starting one-time arbitrage opportunity scan (config: %s)...", configFile))
 
 	// Initialize provider manager for scanning
 	providerManager, err := transport.NewUnifiedProviderManager("config/providers.yaml")