add retroactive check for yesterday's missed habits on /today

Users often only realize a habit was missed the next day; a same-day-only
check made it impossible to record it after the fact.

app/routers/pages.py

@@ -51,6 +51,7 @@ def _today_context(db: Session, user_id: int, **extra) -> dict:
     return {
         "build_items": build_items,
         "quit_items": quit_items,
+        "yesterday_missed": log_service.get_yesterday_missed_items(db, user_id),
         "total_count": len(all_items),
         "checked_count": sum(1 for item in all_items if item.checked),
         **extra,
@@ -89,6 +90,26 @@ def toggle_today_page(request: Request, habit_id: int, db: Session = Depends(get
     )
 
 
+@router.post("/today/{habit_id}/toggle-yesterday")
+def toggle_yesterday_page(request: Request, habit_id: int, db: Session = Depends(get_db)):
+    current = _current_user_or_redirect(request, db)
+    if isinstance(current, RedirectResponse):
+        return current
+
+    habit = habit_service.get_habit(db, habit_id, current.id)
+    if habit is None:
+        return Response(status_code=404)
+
+    yesterday = date.today() - timedelta(days=1)
+    _, milestone_streak = log_service.toggle_check_and_celebrate(db, habit, yesterday)
+    extra = {"celebrate_habit_name": habit.name, "celebrate_streak": milestone_streak} if milestone_streak else {}
+    return templates.TemplateResponse(
+        request,
+        "partials/today_content.html",
+        {"logged_in": True, "current_user": current, **_today_context(db, current.id, **extra)},
+    )
+
+
 @router.get("/habits")
 def habits_page(request: Request, tab: str = "build", db: Session = Depends(get_db)):
     current = _current_user_or_redirect(request, db)