fix(crypto-tail): 监控分时图推送节流与前端采样，避免1s内多条数据导致点过密

- 后端: price_change 推送节流，每策略 1s 内最多推送 1 次，其余靠定时 1.5s 推送补足
- 前端: 同周期内分时图追加点时至少间隔 1s 才追加，保证曲线连续且不过密
- 最新价等展示仍实时更新，仅图表序列做采样

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/src/main/kotlin/com/wrbug/polymarketbot/service/cryptotail/CryptoTailMonitorService.kt

@@ -97,6 +97,10 @@ class CryptoTailMonitorService(
     private val strategyHistoryPeriod = ConcurrentHashMap<Long, Long>()
     private val maxHistorySize = 300
 
+    /** price_change 推送节流：每策略最近一次推送时间，1s 内不重复推送 */
+    private val lastPriceChangePushTime = ConcurrentHashMap<Long, Long>()
+    private val priceChangePushThrottleMs = 1_000L
+
     data class MonitorEntry(
         val strategyId: Long,
         val strategy: CryptoTailStrategy,
@@ -652,8 +656,13 @@ class CryptoTailMonitorService(
 
             strategyPriceData[strategy.id!!] = newPriceData
 
-            val pushData = buildPushData(strategy, newPriceData)
-            addToHistoryAndPush(strategy.id!!, pushData)
+            val now = System.currentTimeMillis()
+            val last = lastPriceChangePushTime[strategy.id!!] ?: 0L
+            if (now - last >= priceChangePushThrottleMs) {
+                lastPriceChangePushTime[strategy.id!!] = now
+                val pushData = buildPushData(strategy, newPriceData)
+                addToHistoryAndPush(strategy.id!!, pushData)
+            }
         }
     }