refactor(biz): 优化模板参数过滤逻辑

- 统计每个占位符在模板中出现的次数
- 根据占位符出现次数和实际可用源数量，选择合适的源进行过滤
- 优化日志输出，增加占位符统计信息

src/main/java/com/ycwl/basic/biz/TemplateBiz.java

@@ -14,6 +14,7 @@ import lombok.extern.slf4j.Slf4j;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Component;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
@@ -134,26 +135,42 @@ public class TemplateBiz {
             return Map.of();
         }
 
+        // 统计每个 placeholder 在模板中出现的次数
+        Map<String, Long> placeholderCounts = templatePlaceholders.stream()
+                .collect(Collectors.groupingBy(
+                        placeholder -> placeholder,
+                        Collectors.counting()
+                ));
+
         Map<String, List<SourceEntity>> filteredParams = new HashMap<>();
 
-        for (String placeholder : templatePlaceholders) {
+        for (Map.Entry<String, Long> entry : placeholderCounts.entrySet()) {
+            String placeholder = entry.getKey();
+            Long requiredCount = entry.getValue();
+
             if (placeholder.startsWith("P")) {
                 // 图片源：占位符格式为 "P{deviceId}"
                 String imageKey = placeholder;
                 if (allTaskParams.containsKey(imageKey)) {
-                    filteredParams.put(imageKey, allTaskParams.get(imageKey));
+                    List<SourceEntity> allSources = allTaskParams.get(imageKey);
+                    int actualCount = Math.min(requiredCount.intValue(), allSources.size());
+                    List<SourceEntity> selectedSources = allSources.subList(0, actualCount);
+                    filteredParams.put(imageKey, new ArrayList<>(selectedSources));
                 }
             } else {
                 // 视频源：占位符直接对应设备ID
                 String videoKey = placeholder;
                 if (allTaskParams.containsKey(videoKey)) {
-                    filteredParams.put(videoKey, allTaskParams.get(videoKey));
+                    List<SourceEntity> allSources = allTaskParams.get(videoKey);
+                    int actualCount = Math.min(requiredCount.intValue(), allSources.size());
+                    List<SourceEntity> selectedSources = allSources.subList(0, actualCount);
+                    filteredParams.put(videoKey, new ArrayList<>(selectedSources));
                 }
             }
         }
 
-        log.info("filterTaskParams: templateId:{}, original keys:{}, filtered keys:{}", 
-                templateId, allTaskParams.keySet().size(), filteredParams.keySet().size());
+        log.info("filterTaskParams: templateId:{}, original keys:{}, filtered keys:{}, placeholder counts:{}", 
+                templateId, allTaskParams.keySet().size(), filteredParams.keySet().size(), placeholderCounts);
         
         return filteredParams;
     }