Add TimeSelector and ScheduleModal components with tests

- Implemented TimeSelector component for selecting time with AM/PM toggle and minute/hour increment/decrement functionality.
- Created ScheduleModal component for scheduling chores with options for specific days or intervals.
- Added utility functions for scheduling logic in scheduleUtils.ts.
- Developed comprehensive tests for TimeSelector and scheduleUtils functions to ensure correct behavior.

backend/models/task_extension.py

@@ -0,0 +1,29 @@
+from dataclasses import dataclass
+from models.base import BaseModel
+
+
+@dataclass
+class TaskExtension(BaseModel):
+    child_id: str
+    task_id: str
+    date: str   # ISO date string supplied by client, e.g. '2026-02-22'
+
+    @classmethod
+    def from_dict(cls, d: dict) -> 'TaskExtension':
+        return cls(
+            child_id=d.get('child_id'),
+            task_id=d.get('task_id'),
+            date=d.get('date'),
+            id=d.get('id'),
+            created_at=d.get('created_at'),
+            updated_at=d.get('updated_at'),
+        )
+
+    def to_dict(self) -> dict:
+        base = super().to_dict()
+        base.update({
+            'child_id': self.child_id,
+            'task_id': self.task_id,
+            'date': self.date,
+        })
+        return base