Add chore expiry notification system with scheduling and tests

- Implemented `trigger_chore_expiry.py` script to manually trigger chore expiry notifications for users via the admin API.
- Developed `chore_expiry_notification_scheduler.py` to handle the logic for sending notifications for chores expiring within the next 75 minutes.
- Created utility functions in `schedule_utils.py` to determine scheduling and deadlines for chores.
- Added comprehensive tests for the chore expiry notification system in `test_chore_expiry_notification_scheduler.py`, covering various scenarios including scheduled chores, confirmations, and user settings.

backend/utils/schedule_utils.py

@@ -0,0 +1,91 @@
+"""
+Python port of the frontend schedule logic in scheduleUtils.ts.
+
+These utilities determine whether a chore is scheduled on a given day and what
+its deadline time is.  The frontend is the source of truth for schedule math;
+keep this file in sync with any changes to scheduleUtils.ts.
+"""
+
+from datetime import date
+
+
+def interval_hits_today(anchor_date: str, interval_days: int, local_date: date) -> bool:
+    """Return True if an interval-mode schedule fires on local_date.
+
+    anchor_date: ISO date string e.g. "2026-02-25", or "" (backward compat →
+                 treats local_date itself as anchor, so it always hits today and
+                 every interval_days days after).
+    Dates before the anchor always return False (scheduling hasn't started yet).
+    """
+    if anchor_date:
+        parts = anchor_date.split('-')
+        anchor = date(int(parts[0]), int(parts[1]), int(parts[2]))
+    else:
+        # Empty anchor = start from today (backward compat)
+        anchor = local_date
+
+    diff_days = (local_date - anchor).days
+    if diff_days < 0:
+        return False
+    return diff_days % interval_days == 0
+
+
+def is_scheduled_today(schedule: dict, local_date: date) -> bool:
+    """Return True if the schedule applies on local_date.
+
+    - days mode: today's weekday (0=Sun … 6=Sat) is in day_configs
+    - interval mode: interval_hits_today
+    - paused (enabled=False): always True (chore shows every day, like no schedule)
+    """
+    if not schedule.get('enabled', True):
+        return True  # paused = show always, like an unscheduled chore
+
+    mode = schedule.get('mode', 'days')
+    if mode == 'days':
+        # Python's weekday(): Mon=0..Sun=6. Our convention: Sun=0..Sat=6 (JS/TS).
+        # Convert: js_day = (python_weekday + 1) % 7
+        js_weekday = (local_date.weekday() + 1) % 7
+        day_configs = schedule.get('day_configs', [])
+        return any(dc.get('day') == js_weekday for dc in day_configs)
+    else:
+        return interval_hits_today(
+            schedule.get('anchor_date', ''),
+            schedule.get('interval_days', 2),
+            local_date,
+        )
+
+
+def get_due_time_today(schedule: dict, local_date: date) -> tuple[int, int] | None:
+    """Return (hour, minute) for the deadline today, or None if no deadline applies.
+
+    Returns None when:
+    - The schedule is paused (enabled=False) — no deadline, acts like Anytime
+    - The day is not scheduled
+    - The schedule has no deadline (default_has_deadline=False or
+      interval_has_deadline=False → 'Anytime')
+
+    Callers treat None as 'active all day with no expiry'.
+    """
+    if not schedule.get('enabled', True):
+        return None  # paused = no deadline, no expiry
+
+    mode = schedule.get('mode', 'days')
+    if mode == 'days':
+        if not schedule.get('default_has_deadline', True):
+            return None  # Anytime
+        js_weekday = (local_date.weekday() + 1) % 7
+        day_configs = schedule.get('day_configs', [])
+        dc = next((d for d in day_configs if d.get('day') == js_weekday), None)
+        if dc is None:
+            return None
+        return (dc.get('hour', 0), dc.get('minute', 0))
+    else:
+        if not interval_hits_today(
+            schedule.get('anchor_date', ''),
+            schedule.get('interval_days', 2),
+            local_date,
+        ):
+            return None
+        if not schedule.get('interval_has_deadline', True):
+            return None  # Anytime
+        return (schedule.get('interval_hour', 0), schedule.get('interval_minute', 0))