fix: use exclusive end-time boundary in office hours check

time <= amEnd incorrectly allowed 12:00 when the office closes at 12:00.
Changed to time < amEnd (and time < pmEnd) so the session end time is
treated as a closed boundary — a patient cannot start an appointment at
exactly the time the session ends.

Fixes both the SMS reschedule flow and the schedule grid slot highlighting.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/Backend/src/ai/reschedule-graph.ts

@@ -271,8 +271,8 @@ async function isWithinOfficeHours(
       const slot = group?.[dayName];
       if (!slot?.enabled) continue;
       if (
-        (time >= slot.amStart && time <= slot.amEnd) ||
-        (time >= slot.pmStart && time <= slot.pmEnd)
+        (time >= slot.amStart && time < slot.amEnd) ||
+        (time >= slot.pmStart && time < slot.pmEnd)
       ) return true;
     }
     return false;