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.

reaction_board/analytics.py

@@ -340,6 +340,29 @@ def compute_growth(
     )
 
 
+def smoothed_growth_rate(
+    delta: int | float | None,
+    previous: int | float | None,
+    prior: int | float,
+) -> float | None:
+    """增速榜排序分：``Δ / (基线 + prior)``。
+
+    ``rate`` 仍是真实相对增速。``prior`` 只削弱小基数在排序里的优势。
+    """
+    if delta is None or previous is None or isinstance(delta, bool) or isinstance(previous, bool):
+        return None
+    if isinstance(prior, bool):
+        return None
+    try:
+        strength = float(prior)
+        base = max(0, int(previous)) + strength
+    except (TypeError, ValueError):
+        return None
+    if strength < 0 or base <= 0:
+        return None
+    return int(delta) / base
+
+
 def normalize_cover(url: object) -> str | None:
     """把 B 站封面统一为 https；空值返回 None。"""
     if not isinstance(url, str):