[BUG][LOW] Timezone-unaware datetimes in schedule overlap checks

[kambiz-aghaiepour]

Description

The schedule overlap check in is_host_available and other schedule-related functions use datetime.now() (timezone-unaware) while the schedule records use timezone-aware datetimes (created by parse_date which attaches UTC).

Comparing timezone-naive and timezone-aware datetimes can produce incorrect results or TypeError depending on the Python/sqlalchemy configuration.

Affected Code

• src/quads/server/blueprints/schedules.py:447-454
• src/quads/server/dao/schedule.py:263-267 (parse_date returns timezone-aware)
• src/quads/server/blueprints/schedules.py:241-246 (datetime.now() is timezone-unaware)

Impact

• Schedule overlap checks may produce false negatives
• Possible TypeError on comparison

Recommended Fix

Use datetime.now(timezone.utc) or datetime.utcnow() consistently throughout, or use a utility function that always returns timezone-aware datetimes.

[sadsfae]

The deciding factor here is server timezone (in our case always UTC). I don't think this is a concern but cc: @grafuls for his take.

[grafuls]

I don't think this is a concerning matter as we only use quads from inside the quads host and self schedules do not pass start or end and that is handled by the quads server itself.
This is still a very easy to fix issue so no harm in doing so.