fix(growth): rank the rate board by a smoothed score

Show the real percentage on the card, but sort with delta / (baseline + prior) so a small baseline cannot dominate. Same-day publishes stay off the rate board.

config.example.jsonc

@@ -123,5 +123,7 @@
     "shrink_minutes": null,
     // "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,
   },
 }