平台推荐排序公式 v4: 时间衰减系数 0.9 → 0.8

- 近 3 天权重占比从 28% 提升至 50%，近 7 天从 54% 提升至 75%
- PROD 验证 (aggDt=20260510)：Top 100 中 1-14 天新内容从 16 个增至 29 个，长尾老视频(22-30 天无近期热度)相应下沉；Top 7 几乎不变，无节日内容或仅 1-3 天数据视频污染 Top 20

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

api-module/src/main/resources/mapper/contentplatform/ext/ContentPlatformPlanMapperExt.xml

@@ -264,7 +264,7 @@
         FROM (
         SELECT video_id, category, title, cover, video,
             SUM(IFNULL(rovn, 0) * (1 + LN(GREATEST(IFNULL(exposure, 0) / 5000.0, 1.0)))
-                * POWER(0.9, DATEDIFF(STR_TO_DATE(#{aggDt}, '%Y%m%d'), STR_TO_DATE(dt, '%Y%m%d'))))
+                * POWER(0.8, DATEDIFF(STR_TO_DATE(#{aggDt}, '%Y%m%d'), STR_TO_DATE(dt, '%Y%m%d'))))
                 OVER (PARTITION BY video_id) AS weighted_score,
             ROW_NUMBER() OVER (PARTITION BY video_id ORDER BY dt DESC) AS rn
         FROM content_platform_video