Complete frontend migration to shared VEvent model

- Update frontend to use shared calendar-models library
- Add display methods to VEvent for UI compatibility
- Remove duplicate VEvent definitions in frontend
- Fix JSON field name mismatch (dtstart/dtend vs start/end)
- Create CalendarEvent type alias for backward compatibility
- Resolve "missing field start" parsing error

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

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

calendar-models/src/vevent.rs

@@ -146,4 +146,38 @@ impl VEvent {
     pub fn is_exception(&self) -> bool {
         self.recurrence_id.is_some()
     }
+
+    /// Get display string for status
+    pub fn get_status_display(&self) -> &'static str {
+        match &self.status {
+            Some(EventStatus::Tentative) => "Tentative",
+            Some(EventStatus::Confirmed) => "Confirmed", 
+            Some(EventStatus::Cancelled) => "Cancelled",
+            None => "Confirmed", // Default
+        }
+    }
+
+    /// Get display string for class
+    pub fn get_class_display(&self) -> &'static str {
+        match &self.class {
+            Some(EventClass::Public) => "Public",
+            Some(EventClass::Private) => "Private",
+            Some(EventClass::Confidential) => "Confidential",
+            None => "Public", // Default
+        }
+    }
+
+    /// Get display string for priority
+    pub fn get_priority_display(&self) -> String {
+        match self.priority {
+            None => "Not set".to_string(),
+            Some(0) => "Undefined".to_string(),
+            Some(1) => "High".to_string(),
+            Some(p) if p <= 4 => "High".to_string(),
+            Some(5) => "Medium".to_string(),
+            Some(p) if p <= 8 => "Low".to_string(),
+            Some(9) => "Low".to_string(),
+            Some(p) => format!("Priority {}", p),
+        }
+    }
 }