Implement custom reminders with multiple VAlarms per event

Major Features:
- Replace single ReminderType enum with Vec<VAlarm> throughout stack
- Add comprehensive alarm management UI with AlarmList and AddAlarmModal components
- Support relative (15min before, 2hrs after) and absolute (specific date/time) triggers
- Display reminder icons in both month and week calendar views
- RFC 5545 compliant VALARM implementation using calendar-models library

Frontend Changes:
- Create AlarmList component for displaying configured reminders
- Create AddAlarmModal with full alarm configuration (trigger, timing, description)
- Update RemindersTab to use new alarm management interface
- Replace old ReminderType dropdown with modern multi-alarm system
- Add reminder icons to event displays in month/week views
- Fix event title ellipsis behavior in week view with proper CSS constraints

Backend Changes:
- Update all request/response models to use Vec<VAlarm> instead of String
- Remove EventReminder conversion logic, pass VAlarms directly through
- Maintain RFC 5545 compliance for CalDAV server compatibility

UI/UX Improvements:
- Improved basic details tab layout (calendar/repeat side-by-side, All Day checkbox repositioned)
- Simplified reminder system to single notification type for user clarity
- Font Awesome icons throughout instead of emojis for consistency
- Clean modal styling with proper button padding and hover states
- Removed non-standard custom message fields for maximum CalDAV compatibility

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

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

frontend/src/components/week_view.rs

@@ -968,7 +968,12 @@ pub fn week_view(props: &WeekViewProps) -> Html {
 
                                                                 // Event content
                                                                 <div class="event-content">
-                                                                    <div class="event-title">{event.summary.as_ref().unwrap_or(&"Untitled".to_string())}</div>
+                                                                    <div class="event-title-row">
+                                                                        <span class="event-title">{event.summary.as_ref().unwrap_or(&"Untitled".to_string())}</span>
+                                                                        if !event.alarms.is_empty() {
+                                                                            <i class="fas fa-bell event-reminder-icon" title="Has reminders"></i>
+                                                                        }
+                                                                    </div>
                                                                     {if !is_all_day && duration_pixels > 30.0 {
                                                                         html! { <div class="event-time">{time_display}</div> }
                                                                     } else {