feat: add production deployment config

- Add docker-compose.prod.yml with env var support
- Add frontend/Dockerfile.prod with nginx for static serving
- Fix Zulip notification to run in thread pool (avoid blocking)
- Use Zulip time format for timezone-aware display
- Add Zulip @mentions for users matched by email

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/app/main.py

@@ -1,3 +1,4 @@
+import asyncio
 import logging
 from uuid import UUID
 
@@ -146,7 +147,6 @@ async def sync_participant(participant_id: UUID, db: AsyncSession = Depends(get_
 async def schedule_meeting(
     data: ScheduleRequest, db: AsyncSession = Depends(get_db)
 ):
-    # 1. Validate Lead Time (2 hours)
     min_start_time = datetime.now(timezone.utc) + timedelta(hours=2)
     if data.start_time.replace(tzinfo=timezone.utc) < min_start_time:
         raise HTTPException(
@@ -154,7 +154,6 @@ async def schedule_meeting(
             detail="Meetings must be scheduled at least 2 hours in advance."
         )
 
-    # 2. Fetch Participants
     result = await db.execute(
         select(Participant).where(Participant.id.in_(data.participant_ids))
     )
@@ -166,9 +165,7 @@ async def schedule_meeting(
     participant_dicts = [
         {"name": p.name, "email": p.email} for p in participants
     ]
-    participant_names = [p.name for p in participants]
 
-    # 3. Send Notifications
     email_success = await send_meeting_invite(
         participant_dicts,
         data.title,
@@ -177,10 +174,11 @@ async def schedule_meeting(
         data.end_time
     )
 
-    zulip_success = send_zulip_notification(
+    zulip_success = await asyncio.to_thread(
+        send_zulip_notification,
         data.title,
         data.start_time,
-        participant_names
+        participant_dicts
     )
 
     return {