fix(growth): require a 1000-view baseline on the rate board

Keep small-base videos on the delta board only, and raise the smoothing prior to 1000 so videos that just clear the floor do not dominate the ranking.

config.example.jsonc

@@ -124,6 +124,6 @@
     // "auto" = 7 日有数据用 7，否则 1
     "home_growth_days": "auto",
     // 增速榜排序：Δ / (基线 + prior)。卡片上的百分比仍是 Δ / 基线。
-    "growth_rate_prior": 500,
+    "growth_rate_prior": 1000,
   },
 }