fix(market): prevent program crash on WebSocket failure

## Problem
- Program crashes with log.Fatalf when WebSocket connection fails
- Triggered by WebSocket hijacking issue (157.240.12.50)
- Introduced in commit 3b1db6f (K-line WebSocket migration)
## Solution
- Replace 4x log.Fatalf with log.Printf in monitor.go
- Lines 177, 183, 189, 215
- Program now logs error and continues running
## Changes
1. Initialize failure: Fatalf → Printf (line 177)
2. Connection failure: Fatalf → Printf (line 183)
3. Subscribe failure: Fatalf → Printf (line 189)
4. K-line subscribe: Fatalf → Printf + dynamic period (line 215)
## Fallback
- System automatically uses API when WebSocket cache is empty
- GetCurrentKlines() has built-in degradation mechanism
- No data loss, slightly slower API calls as fallback
## Impact
- ✅ Program stability: Won't crash on network issues
- ✅ Error visibility: Clear error messages in logs
- ✅ Data integrity: API fallback ensures K-line availability
Related: websocket-hijack-fix.md, auto-stop-bug-analysis.md

market/monitor.go

@@ -121,19 +121,19 @@ func (m *WSMonitor) Start(coins []string) {
 	// 初始化交易对
 	err := m.Initialize(coins)
 	if err != nil {
-		log.Fatalf("❌ 初始化币种: %v", err)
+		log.Printf("❌ 初始化币种失败: %v", err)
 		return
 	}
 
 	err = m.combinedClient.Connect()
 	if err != nil {
-		log.Fatalf("❌ 批量订阅流: %v", err)
+		log.Printf("❌ 批量订阅流失败: %v", err)
 		return
 	}
 	// 订阅所有交易对
 	err = m.subscribeAll()
 	if err != nil {
-		log.Fatalf("❌ 订阅币种交易对: %v", err)
+		log.Printf("❌ 订阅币种交易对失败: %v", err)
 		return
 	}
 }
@@ -159,7 +159,7 @@ func (m *WSMonitor) subscribeAll() error {
 	for _, st := range subKlineTime {
 		err := m.combinedClient.BatchSubscribeKlines(m.symbols, st)
 		if err != nil {
-			log.Fatalf("❌ 订阅3m K线: %v", err)
+			log.Printf("❌ 订阅 %s K线失败: %v", st, err)
 			return err
 		}
 	}