Implement complete recurring event deletion with EXDATE and RRULE UNTIL support

Frontend Changes:
- Add DeleteAction enum with DeleteThis, DeleteFollowing, DeleteSeries options
- Update EventContextMenu to show different delete options for recurring events
- Add exception_dates field to CalendarEvent struct
- Fix occurrence generation to respect EXDATE exclusions
- Add comprehensive RRULE parsing with UNTIL date support
- Fix UNTIL date parsing to handle backend format (YYYYMMDDTHHMMSSZ)
- Enhanced debugging for RRULE processing and occurrence generation

Backend Changes:
- Add exception_dates field to CalendarEvent struct with EXDATE parsing/generation
- Implement update_event method for CalDAV client
- Add fetch_event_by_href helper function
- Update DeleteEventRequest model with delete_action and occurrence_date fields
- Implement proper delete_this logic with EXDATE addition
- Implement delete_following logic with RRULE UNTIL modification
- Add comprehensive logging for delete operations

CalDAV Integration:
- Proper EXDATE generation in iCal format for excluded occurrences
- RRULE modification with UNTIL clause for partial series deletion
- Event updating via CalDAV PUT operations
- Full iCal RFC 5545 compliance for recurring event modifications

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

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

backend/src/calendar.rs

@@ -50,6 +50,9 @@ pub struct CalendarEvent {
     /// Recurrence rule (RRULE)
     pub recurrence_rule: Option<String>,
     
+    /// Exception dates - dates to exclude from recurrence (EXDATE)
+    pub exception_dates: Vec<DateTime<Utc>>,
+    
     /// All-day event flag
     pub all_day: bool,
     
@@ -361,6 +364,9 @@ impl CalDAVClient {
         let last_modified = properties.get("LAST-MODIFIED")
             .and_then(|s| self.parse_datetime(s, None).ok());
 
+        // Parse exception dates (EXDATE)
+        let exception_dates = self.parse_exception_dates(&event);
+
         Ok(CalendarEvent {
             uid,
             summary: properties.get("SUMMARY").cloned(),
@@ -377,6 +383,7 @@ impl CalDAVClient {
             created,
             last_modified,
             recurrence_rule: properties.get("RRULE").cloned(),
+            exception_dates,
             all_day,
             reminders: self.parse_alarms(&event)?,
             etag: None, // Set by caller
@@ -591,6 +598,28 @@ impl CalDAVClient {
         Err(CalDAVError::ParseError(format!("Unable to parse datetime: {}", datetime_str)))
     }
 
+    /// Parse EXDATE properties from an iCal event
+    fn parse_exception_dates(&self, event: &ical::parser::ical::component::IcalEvent) -> Vec<DateTime<Utc>> {
+        let mut exception_dates = Vec::new();
+        
+        // Look for EXDATE properties
+        for property in &event.properties {
+            if property.name.to_uppercase() == "EXDATE" {
+                if let Some(value) = &property.value {
+                    // EXDATE can contain multiple comma-separated dates
+                    for date_str in value.split(',') {
+                        // Try to parse the date (the parse_datetime method will handle different formats)
+                        if let Ok(date) = self.parse_datetime(date_str.trim(), None) {
+                            exception_dates.push(date);
+                        }
+                    }
+                }
+            }
+        }
+        
+        exception_dates
+    }
+
     /// Create a new calendar on the CalDAV server using MKCALENDAR
     pub async fn create_calendar(&self, name: &str, description: Option<&str>, color: Option<&str>) -> Result<(), CalDAVError> {
         // Sanitize calendar name for URL path
@@ -758,6 +787,56 @@ impl CalDAVClient {
         }
     }
 
+    /// Update an existing event on the CalDAV server
+    pub async fn update_event(&self, calendar_path: &str, event: &CalendarEvent, event_href: &str) -> Result<(), CalDAVError> {
+        // Construct the full URL for the event
+        let full_url = if event_href.starts_with("http") {
+            event_href.to_string()
+        } else if event_href.starts_with("/dav.php") {
+            // Event href is already a full path, combine with base server URL (without /dav.php)
+            let base_url = self.config.server_url.trim_end_matches('/').trim_end_matches("/dav.php");
+            format!("{}{}", base_url, event_href)
+        } else {
+            // Event href is just a filename, combine with calendar path
+            let clean_path = if calendar_path.starts_with("/dav.php") {
+                calendar_path.trim_start_matches("/dav.php")
+            } else {
+                calendar_path
+            };
+            format!("{}/dav.php{}/{}", self.config.server_url.trim_end_matches('/'), clean_path, event_href)
+        };
+        
+        println!("📝 Updating event at: {}", full_url);
+        
+        // Generate iCalendar data for the event
+        let ical_data = self.generate_ical_event(event)?;
+        
+        println!("📝 Updated iCal data: {}", ical_data);
+        println!("📝 Event has {} exception dates", event.exception_dates.len());
+        
+        let response = self.http_client
+            .put(&full_url)
+            .header("Authorization", format!("Basic {}", self.config.get_basic_auth()))
+            .header("Content-Type", "text/calendar; charset=utf-8")
+            .header("User-Agent", "calendar-app/0.1.0")
+            .body(ical_data)
+            .send()
+            .await
+            .map_err(|e| CalDAVError::ParseError(e.to_string()))?;
+
+        println!("Event update response status: {}", response.status());
+        
+        if response.status().is_success() || response.status().as_u16() == 201 || response.status().as_u16() == 204 {
+            println!("✅ Event updated successfully");
+            Ok(())
+        } else {
+            let status = response.status();
+            let error_body = response.text().await.unwrap_or_default();
+            println!("❌ Event update failed: {} - {}", status, error_body);
+            Err(CalDAVError::ServerError(status.as_u16()))
+        }
+    }
+
     /// Generate iCalendar data for a CalendarEvent
     fn generate_ical_event(&self, event: &CalendarEvent) -> Result<String, CalDAVError> {
         let now = chrono::Utc::now();
@@ -871,6 +950,15 @@ impl CalDAVClient {
             ical.push_str(&format!("RRULE:{}\r\n", rrule));
         }
         
+        // Exception dates (EXDATE)
+        for exception_date in &event.exception_dates {
+            if event.all_day {
+                ical.push_str(&format!("EXDATE;VALUE=DATE:{}\r\n", format_date(exception_date)));
+            } else {
+                ical.push_str(&format!("EXDATE:{}\r\n", format_datetime(exception_date)));
+            }
+        }
+        
         ical.push_str("END:VEVENT\r\n");
         ical.push_str("END:VCALENDAR\r\n");