feat(backend): consolidate queue logic for scheduling

backend/database/models/schedule.py

@@ -0,0 +1,17 @@
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Optional
+from ._base import BaseModel
+
+
+@dataclass
+class Schedule(BaseModel):
+    ScheduleId: int
+    ServiceId: int
+    MemberId: int
+    Status: str                     # 'pending' | 'accepted' | 'declined'
+    ScheduledAt: datetime           # renamed from OfferedAt
+    AcceptedAt: Optional[datetime] = None
+    DeclinedAt: Optional[datetime] = None
+    ExpiresAt: Optional[datetime] = None
+    DeclineReason: Optional[str] = None