Score each metric on the average of its seasonal differentials (#200)

Annual scores were computed from an all-year pooled distribution, which widens
the reference spread and hides a shift confined to one season — Seattle's daily
high read 16 despite a summer high of 65. Build each metric's annual score
(and the overall) as the mean of its four seasonal divergences instead, so a
real seasonal shift shows through (that high now reads 28). Frequency read-outs
(precip wet days, wet-bulb heat-stress days) stay pooled over the year.

Also lock the by-season table to fixed, uniform columns (min-width to scroll on
a phone) so each metric lines up vertically across the seasons, and show the
per-percentile detail as the season-averaged shift.

Bumps the score cache version.

scoring.py

@@ -230,6 +230,56 @@ def _overall(entries: dict) -> dict | None:
             "tier": tier, "class": css, "grade": tier, "descriptor": "net change"}
 
 
+def _slice_entry(metric: str, history: pl.DataFrame, base_s: pl.DataFrame,
+                 rec_s: pl.DataFrame) -> dict:
+    if metric not in history.columns:
+        return _null_entry(metric, "not available for this location")
+    return _metric_entry(metric, grading._finite(base_s[metric]), grading._finite(rec_s[metric]))
+
+
+def _annual_entry(metric: str, seasonal: list, history: pl.DataFrame,
+                  baseline: pl.DataFrame, recent: pl.DataFrame) -> dict:
+    """The metric's headline score, built as the AVERAGE of its seasonal
+    differentials rather than from an annually-pooled distribution. Pooling all
+    days together widens the reference spread and hides a shift confined to one
+    season (a hot-summer trend barely moves the all-year percentiles); averaging
+    the four seasons' divergences keeps it visible. Frequency read-outs
+    (precip wet days, wet-bulb heat-stress days) are day counts, so those stay
+    pooled over the whole year."""
+    if metric not in history.columns:
+        return _null_entry(metric, "not available for this location")
+    present = [e for e in seasonal if e.get("score") is not None]
+    if not present:
+        return _null_entry(metric, "not enough recent data")
+    mad = sum(e["mad"] for e in present) / len(present)
+    bias = sum(e["bias"] for e in present) / len(present)
+    score = score_of(mad)
+    tier, css = tier_of(score, bias)
+    direction = _direction(metric, bias)
+    per_q = []
+    for q in QS:
+        ds = [pq["d"] for e in present for pq in e.get("per_q", []) if pq["q"] == q]
+        if ds:
+            per_q.append({"q": q, "d": round(sum(ds) / len(ds), 1)})
+    entry = {
+        "key": metric, "label": METRIC_LABELS[metric],
+        "score": score, "mad": round(mad, 1), "bias": round(bias, 1),
+        "tier": tier, "class": css, "direction": direction,
+        "grade": tier if score < 15 else f"{tier} — {direction}",
+        "weight": WEIGHTS[metric], "per_q": per_q,
+        "n_recent": sum(e["n_recent"] for e in present),
+        "n_base": sum(e["n_base"] for e in present),
+    }
+    if metric == "precip":
+        div = precip_divergence(grading._finite(baseline["precip"]), grading._finite(recent["precip"]))
+        if div:
+            entry["freq"] = div["freq"]
+    elif metric == "wetbulb":
+        entry["freq"] = _stress_freq(grading._finite(baseline["wetbulb"]),
+                                     grading._finite(recent["wetbulb"]), WETBULB_STRESS_F)
+    return entry
+
+
 def build_scores(history: pl.DataFrame) -> dict:
     """Full score payload for a cell's history frame. Returns an ``{"unavailable":
     reason}`` shape when the record is too short to score."""
@@ -241,17 +291,20 @@ def build_scores(history: pl.DataFrame) -> dict:
     recent, baseline = recent_baseline_split(history)
     latest = history["date"].max()
 
+    # Each season scored on its own distribution first…
     slices = {}
-    for key in SLICES:
+    for key in SEASONS:
         base_s, rec_s = _slice(baseline, key), _slice(recent, key)
-        entries = {}
-        for m in SCORE_METRICS:
-            if m not in history.columns:
-                entries[m] = _null_entry(m, "not available for this location")
-                continue
-            entries[m] = _metric_entry(m, grading._finite(base_s[m]), grading._finite(rec_s[m]))
+        entries = {m: _slice_entry(m, history, base_s, rec_s) for m in SCORE_METRICS}
         slices[key] = {"overall": _overall(entries), "metrics": entries}
 
+    # …then the annual headline is the average of those seasonal differentials.
+    annual = {}
+    for m in SCORE_METRICS:
+        seasonal = [slices[k]["metrics"][m] for k in SEASONS]
+        annual[m] = _annual_entry(m, seasonal, history, baseline, recent)
+    slices = {"annual": {"overall": _overall(annual), "metrics": annual}, **slices}
+
     return {
         "recent_years": RECENT_YEARS,
         "recent_range": [recent["date"].min().isoformat(), latest.isoformat()],

views.py

@@ -108,7 +108,7 @@ def forecast_key(today, days: int) -> str:
 # is the plain `history_token` (expires when the archive tail advances). The key
 # just carries the scoring-math version, so a math change invalidates only score
 # rows without disturbing any other kind.
-SCORE_VER = "s2"
+SCORE_VER = "s3"
 
 
 def score_key() -> str: