feat(whale-monitor): 市场选择改为弹窗并优化列表交互

- 策略编辑内嵌市场选择弹窗，移除路由跳转与 sessionStorage 草稿
- 列表区固定高度内部滚动，底部仅保留一处确认操作
- 并发缓存 markets 时捕获唯一键冲突并回读已有记录

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

backend/src/main/kotlin/com/wrbug/polymarketbot/service/common/MarketService.kt

@@ -11,6 +11,7 @@ import com.wrbug.polymarketbot.util.getEventSlug
 import com.wrbug.polymarketbot.util.parseStringArray
 import kotlinx.coroutines.runBlocking
 import org.slf4j.LoggerFactory
+import org.springframework.dao.DataIntegrityViolationException
 import org.springframework.stereotype.Service
 import java.time.Instant
 import java.time.format.DateTimeFormatter
@@ -205,9 +206,20 @@ class MarketService(
                 )
             }
             
-            val savedMarket = marketRepository.save(market)
-            marketCache.put(marketId, savedMarket)
-            savedMarket
+            try {
+                val savedMarket = marketRepository.save(market)
+                marketCache.put(marketId, savedMarket)
+                savedMarket
+            } catch (e: DataIntegrityViolationException) {
+                // 并发写入同一个 marketId 时可能触发唯一索引冲突，这里降级为查询并返回已有记录
+                val existingAfter = marketRepository.findByMarketId(marketId)
+                if (existingAfter != null) {
+                    marketCache.put(marketId, existingAfter)
+                    existingAfter
+                } else {
+                    throw e
+                }
+            }
         } catch (e: Exception) {
             logger.error("保存市场信息失败: marketId=$marketId, error=${e.message}", e)
             null