add habit leveling/XP system, explicit fail marking for missed habits, and scrollable habit tabs

- Habits and the account now accumulate XP and levels from check streaks, with
  streak/level-up celebration banners and push notifications.
- The "yesterday missed" banner on /today now lets a habit be explicitly marked
  failed (not just checked done), backed by a new HabitLog.status column so
  completion-rate/streak calculations never count a failed day as done.
- The habit management tabs scroll horizontally on narrow screens instead of
  wrapping to two lines, with a pure-CSS edge shadow indicating more content.

app/routers/pages.py

@@ -14,7 +14,14 @@ from app.models.user import User
 from app.schemas.habit import HabitCreate, HabitUpdate
 from app.security import get_current_user_optional
 from app.services import habit_service, log_service
-from app.template_utils import difficulty_label, goal_progress, heatmap_opacity, is_milestone_streak, weekday_label
+from app.template_utils import (
+    difficulty_label,
+    goal_progress,
+    heatmap_opacity,
+    is_milestone_streak,
+    level_tier_emoji,
+    weekday_label,
+)
 
 router = APIRouter()
 
@@ -24,6 +31,7 @@ templates.env.globals["heatmap_opacity"] = heatmap_opacity
 templates.env.globals["is_milestone_streak"] = is_milestone_streak
 templates.env.globals["difficulty_label"] = difficulty_label
 templates.env.globals["goal_progress"] = goal_progress
+templates.env.globals["level_tier_emoji"] = level_tier_emoji
 templates.env.globals["habit_difficulties"] = list(HabitDifficulty)
 
 
@@ -57,6 +65,7 @@ def _today_context(db: Session, user_id: int, **extra) -> dict:
         "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),
+        "account_level": log_service.get_account_level(db, user_id),
         **extra,
     }
 
@@ -84,8 +93,12 @@ def toggle_today_page(request: Request, habit_id: int, db: Session = Depends(get
     if habit is None:
         return Response(status_code=404)
 
-    _, milestone_streak = log_service.toggle_check_and_celebrate(db, habit, date.today())
-    extra = {"celebrate_habit_name": habit.name, "celebrate_streak": milestone_streak} if milestone_streak else {}
+    _, milestone_streak, level_up = log_service.toggle_check_and_celebrate(db, habit, date.today())
+    extra = {"celebrate_habit_name": habit.name} if (milestone_streak or level_up) else {}
+    if milestone_streak:
+        extra["celebrate_streak"] = milestone_streak
+    if level_up:
+        extra["celebrate_level_up"] = level_up
     return templates.TemplateResponse(
         request,
         "partials/today_content.html",
@@ -104,8 +117,12 @@ def toggle_yesterday_page(request: Request, habit_id: int, db: Session = Depends
         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 {}
+    _, milestone_streak, level_up = log_service.toggle_check_and_celebrate(db, habit, yesterday)
+    extra = {"celebrate_habit_name": habit.name} if (milestone_streak or level_up) else {}
+    if milestone_streak:
+        extra["celebrate_streak"] = milestone_streak
+    if level_up:
+        extra["celebrate_level_up"] = level_up
     return templates.TemplateResponse(
         request,
         "partials/today_content.html",
@@ -113,6 +130,25 @@ def toggle_yesterday_page(request: Request, habit_id: int, db: Session = Depends
     )
 
 
+@router.post("/today/{habit_id}/fail-yesterday")
+def fail_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)
+    log_service.mark_failed(db, habit.id, yesterday)
+    return templates.TemplateResponse(
+        request,
+        "partials/today_content.html",
+        {"logged_in": True, "current_user": current, **_today_context(db, current.id)},
+    )
+
+
 @router.get("/habits")
 def habits_page(request: Request, tab: str = "build", db: Session = Depends(get_db)):
     current = _current_user_or_redirect(request, db)
@@ -140,6 +176,7 @@ def habits_page(request: Request, tab: str = "build", db: Session = Depends(get_
             "habits": habits,
             "habit_type": tab,
             "stats_map": stats_map,
+            "account_level": log_service.get_account_level(db, current.id),
         },
     )
 
@@ -355,5 +392,12 @@ def history_page(
         context = _month_context(db, current.id, year or today.year, month or today.month)
 
     return templates.TemplateResponse(
-        request, "history.html", {"logged_in": True, "current_user": current, **context}
+        request,
+        "history.html",
+        {
+            "logged_in": True,
+            "current_user": current,
+            "account_level": log_service.get_account_level(db, current.id),
+            **context,
+        },
     )