Clean up code to resolve all compiler warnings

- Remove unused AlarmStorage module and all references
- Remove unused imports (AlarmAction, AlarmTrigger, VAlarm from backend)
- Remove unused ReminderType enum from event form types
- Remove unused methods from AlarmScheduler and NotificationManager
- Fix unnecessary mut on NotificationOptions
- Simplify alarm system initialization in app.rs
- Remove unused variable assignments

🤖 Generated with [Claude Code](https://claude.ai/code)

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

backend/src/handlers/events.rs

@@ -16,7 +16,7 @@ use crate::{
     AppState,
 };
 use calendar_models::{
-    AlarmAction, AlarmTrigger, Attendee, CalendarUser, EventClass, EventStatus, VAlarm, VEvent,
+    Attendee, CalendarUser, EventClass, EventStatus, VEvent,
 };
 
 use super::auth::{extract_bearer_token, extract_password_header};