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.docker.example.jsonc

@@ -108,5 +108,6 @@
     "video_shrink_minutes": 60,
     "shrink_minutes": null,
     "home_growth_days": "auto",
+    "growth_rate_prior": 500,
   },
 }