Implement calendar deletion with right-click context menu

Added complete calendar deletion functionality including:
- Context menu component with right-click activation on calendar items
- Backend API endpoint for calendar deletion with CalDAV DELETE method
- Frontend integration with calendar list refresh after deletion
- Fixed URL construction to prevent double /dav.php path issue
- Added proper error handling and user feedback

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

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

backend/src/calendar.rs

@@ -658,6 +658,42 @@ impl CalDAVClient {
             Err(CalDAVError::ServerError(status.as_u16()))
         }
     }
+
+    /// Delete a calendar from the CalDAV server
+    pub async fn delete_calendar(&self, calendar_path: &str) -> Result<(), CalDAVError> {
+        let full_url = if calendar_path.starts_with("http") {
+            calendar_path.to_string()
+        } else {
+            // Handle case where calendar_path already contains /dav.php
+            let clean_path = if calendar_path.starts_with("/dav.php") {
+                calendar_path.trim_start_matches("/dav.php")
+            } else {
+                calendar_path
+            };
+            format!("{}{}", self.config.server_url.trim_end_matches('/'), clean_path)
+        };
+        
+        println!("Deleting calendar at: {}", full_url);
+        
+        let response = self.http_client
+            .delete(&full_url)
+            .header("Authorization", format!("Basic {}", self.config.get_basic_auth()))
+            .send()
+            .await
+            .map_err(|e| CalDAVError::ParseError(e.to_string()))?;
+
+        println!("Calendar deletion response status: {}", response.status());
+        
+        if response.status().is_success() || response.status().as_u16() == 204 {
+            println!("✅ Calendar deleted successfully at {}", calendar_path);
+            Ok(())
+        } else {
+            let status = response.status();
+            let error_body = response.text().await.unwrap_or_default();
+            println!("❌ Calendar deletion failed: {} - {}", status, error_body);
+            Err(CalDAVError::ServerError(status.as_u16()))
+        }
+    }
 }
 
 /// Helper struct for extracting calendar data from XML responses