Add webinar calendar integration and consulting slot blocking

- Fix webinar duration field reference in Calendar (duration_minutes)
- Calculate and display webinar end times in calendar view
- Fetch webinars for selected date in consulting booking
- Block consulting slots that overlap with webinar times
- Show warning when webinars are scheduled on selected date
- Properly handle webinar time range conflicts

This prevents booking conflicts when users try to schedule
consulting sessions during webinar times.

Example: Webinar 20:15-22:15 blocks consulting slots 20:00-22:30

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

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

src/pages/Calendar.tsx

@@ -46,7 +46,7 @@ export default function Calendar() {
     // Fetch webinar events
     const { data: webinars } = await supabase
       .from('products')
-      .select('id, title, event_start, duration')
+      .select('id, title, event_start, duration_minutes')
       .eq('type', 'webinar')
       .eq('is_active', true)
       .gte('event_start', start)
@@ -76,12 +76,16 @@ export default function Calendar() {
     webinars?.forEach(w => {
       if (w.event_start) {
         const eventDate = new Date(w.event_start);
+        const durationMs = (w.duration_minutes || 60) * 60 * 1000;
+        const endDate = new Date(eventDate.getTime() + durationMs);
+
         allEvents.push({
           id: w.id,
           title: w.title,
           type: 'webinar',
           date: format(eventDate, 'yyyy-MM-dd'),
           start_time: format(eventDate, 'HH:mm'),
+          end_time: format(endDate, 'HH:mm'),
         });
       }
     });