fix(forecast): semaines calées sur le référentiel UTC du journal

Les horodatages board_events sont en UTC (SQLite): une fermeture
en soirée locale tombait hors des semaines locales et faussait
le débit hebdomadaire.

app/forecast.py

@@ -7,7 +7,15 @@ date, and are withheld entirely when the journal has no closures
 to learn from — "not enough history" is an answer, too.
 """
 
-from datetime import date, datetime, timedelta
+from datetime import date, datetime, timedelta, timezone
+
+
+def _journal_today() -> date:
+    """'Today' in the journal's frame: board_events stamps are UTC
+    (SQLite datetime('now')), so week buckets anchor to UTC —
+    otherwise closures logged in the local evening (already
+    tomorrow in UTC) fall outside every bucket."""
+    return datetime.now(timezone.utc).date()
 
 MONTHS_FR = [
     "janvier", "février", "mars", "avril", "mai", "juin",
@@ -35,7 +43,7 @@ def _event_date(event: dict) -> date | None:
 def weekly_closures(events: list[dict], weeks: int = 8,
                     today: date | None = None) -> list[dict]:
     """Closure counts per ISO week, oldest first, current week last."""
-    today = today or date.today()
+    today = today or _journal_today()
     current_monday = today - timedelta(days=today.weekday())
     buckets: list[dict] = []
     for i in range(weeks - 1, -1, -1):
@@ -83,7 +91,7 @@ def estimate(remaining: int, weekly: list[dict],
     no throughput to project from, else dates: central (avg rate),
     earliest (best week), latest (worst nonzero week, if any).
     """
-    today = today or date.today()
+    today = today or _journal_today()
     if remaining <= 0:
         return {"done": True}
     stats = throughput_stats(weekly)