improve timezone discovery

backend/src/app/main.py

@@ -15,6 +15,7 @@ from app.schemas import (
     AvailabilityRequest,
     AvailabilityResponse,
     ParticipantCreate,
+    ParticipantUpdate,
     ParticipantResponse,
     SyncResponse,
     ScheduleRequest,
@@ -63,6 +64,7 @@ async def create_participant(
     participant = Participant(
         name=data.name,
         email=data.email,
+        timezone=data.timezone,
         ics_url=data.ics_url,
     )
     db.add(participant)
@@ -95,6 +97,35 @@ async def get_participant(participant_id: UUID, db: AsyncSession = Depends(get_d
     return participant
 
 
+@app.patch("/api/participants/{participant_id}", response_model=ParticipantResponse)
+async def update_participant(
+    participant_id: UUID, data: ParticipantUpdate, db: AsyncSession = Depends(get_db)
+):
+    result = await db.execute(
+        select(Participant).where(Participant.id == participant_id)
+    )
+    participant = result.scalar_one_or_none()
+    if not participant:
+        raise HTTPException(status_code=404, detail="Participant not found")
+
+    if data.timezone is not None:
+        participant.timezone = data.timezone
+    if data.ics_url is not None:
+        participant.ics_url = data.ics_url if data.ics_url else None
+
+    await db.commit()
+    await db.refresh(participant)
+
+    # Re-sync calendar if ICS URL was updated
+    if data.ics_url is not None and participant.ics_url:
+        try:
+            await sync_participant_calendar(db, participant)
+        except Exception as e:
+            logger.warning(f"Calendar sync failed for {participant.email}: {e}")
+
+    return participant
+
+
 @app.delete("/api/participants/{participant_id}")
 async def delete_participant(participant_id: UUID, db: AsyncSession = Depends(get_db)):
     result = await db.execute(