Standardize timezone usage to timezone.utc

- Replaced all UTC imports with timezone imports
- Changed all datetime.now(UTC) to datetime.now(timezone.utc)
- Consistent with booking.py and more explicit about timezone usage
- Updated models.py, routes/auth.py, and routes/invites.py

backend/models.py

@@ -1,4 +1,4 @@
-from datetime import datetime, date, time, UTC
+from datetime import datetime, date, time, timezone
 from enum import Enum as PyEnum
 from typing import TypedDict
 from sqlalchemy import Integer, String, Float, DateTime, Date, Time, ForeignKey, Table, Column, Enum, UniqueConstraint, select
@@ -197,7 +197,7 @@ class SumRecord(Base):
     b: Mapped[float] = mapped_column(Float, nullable=False)
     result: Mapped[float] = mapped_column(Float, nullable=False)
     created_at: Mapped[datetime] = mapped_column(
-        DateTime(timezone=True), default=lambda: datetime.now(UTC)
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )
 
 
@@ -209,7 +209,7 @@ class CounterRecord(Base):
     value_before: Mapped[int] = mapped_column(Integer, nullable=False)
     value_after: Mapped[int] = mapped_column(Integer, nullable=False)
     created_at: Mapped[datetime] = mapped_column(
-        DateTime(timezone=True), default=lambda: datetime.now(UTC)
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )
 
 
@@ -244,7 +244,7 @@ class Invite(Base):
     
     # Timestamps
     created_at: Mapped[datetime] = mapped_column(
-        DateTime(timezone=True), default=lambda: datetime.now(UTC)
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )
     spent_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
     revoked_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
@@ -262,12 +262,12 @@ class Availability(Base):
     start_time: Mapped[time] = mapped_column(Time, nullable=False)
     end_time: Mapped[time] = mapped_column(Time, nullable=False)
     created_at: Mapped[datetime] = mapped_column(
-        DateTime(timezone=True), default=lambda: datetime.now(UTC)
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )
     updated_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), 
-        default=lambda: datetime.now(UTC),
+        default=lambda: datetime.now(timezone.utc),
-        onupdate=lambda: datetime.now(UTC)
+        onupdate=lambda: datetime.now(timezone.utc)
     )
 
 
@@ -290,6 +290,6 @@ class Appointment(Base):
         Enum(AppointmentStatus), nullable=False, default=AppointmentStatus.BOOKED
     )
     created_at: Mapped[datetime] = mapped_column(
-        DateTime(timezone=True), default=lambda: datetime.now(UTC)
+        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )
     cancelled_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)

backend/routes/auth.py

@@ -1,5 +1,5 @@
 """Authentication routes for register, login, logout, and current user."""
-from datetime import datetime, UTC
+from datetime import datetime, timezone
 
 from fastapi import APIRouter, Depends, HTTPException, Response, status
 from sqlalchemy import select
@@ -90,7 +90,7 @@ async def register(
     # Mark invite as spent
     invite.status = InviteStatus.SPENT
     invite.used_by_id = user.id
-    invite.spent_at = datetime.now(UTC)
+    invite.spent_at = datetime.now(timezone.utc)
 
     await db.commit()
     await db.refresh(user)

backend/routes/invites.py

@@ -1,5 +1,5 @@
 """Invite routes for public check, user invites, and admin management."""
-from datetime import datetime, UTC
+from datetime import datetime, timezone
 
 from fastapi import APIRouter, Depends, HTTPException, status, Query
 from sqlalchemy import select, func, desc
@@ -228,7 +228,7 @@ async def revoke_invite(
         )
 
     invite.status = InviteStatus.REVOKED
-    invite.revoked_at = datetime.now(UTC)
+    invite.revoked_at = datetime.now(timezone.utc)
     await db.commit()
     await db.refresh(invite)