Fix recurring event RRULE INTERVAL and COUNT parameter loss

This commit fixes a critical bug where INTERVAL and COUNT parameters
were being stripped from recurring events during backend processing.

Frontend was correctly generating complete RRULE strings like:
FREQ=WEEKLY;INTERVAL=2;BYDAY=TU,FR;COUNT=6

But backend was ignoring the complete RRULE and rebuilding from scratch,
resulting in simplified RRULEs like:
FREQ=WEEKLY;BYDAY=TU,FR (missing INTERVAL and COUNT)

Changes:
- Modified both events and series handlers to detect complete RRULE strings
- Added logic to use frontend RRULE directly when it starts with "FREQ="
- Maintained backwards compatibility with simple recurrence types
- Added comprehensive debug logging for RRULE generation
- Fixed weekly BYDAY occurrence counting to respect COUNT parameter
- Enhanced frontend RRULE generation with detailed logging

This ensures all RFC 5545 RRULE parameters are preserved from
frontend creation through CalDAV storage and retrieval.

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

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

backend/src/handlers/events.rs

@@ -384,29 +384,44 @@ pub async fn create_event(
         }
     };
 
-    // Parse recurrence with BYDAY support for weekly recurrence
-    let rrule = match request.recurrence.to_uppercase().as_str() {
-        "DAILY" => Some("FREQ=DAILY".to_string()),
-        "WEEKLY" => {
-            // Handle weekly recurrence with optional BYDAY parameter
-            let mut rrule = "FREQ=WEEKLY".to_string();
-            
-            // Check if specific days are selected (recurrence_days has 7 elements: [Sun, Mon, Tue, Wed, Thu, Fri, Sat])
-            if request.recurrence_days.len() == 7 {
-                let selected_days: Vec<&str> = request.recurrence_days
-                    .iter()
-                    .enumerate()
-                    .filter_map(|(i, &selected)| {
-                        if selected {
-                            Some(match i {
-                                0 => "SU", // Sunday
-                                1 => "MO", // Monday
-                                2 => "TU", // Tuesday
-                                3 => "WE", // Wednesday
-                                4 => "TH", // Thursday
-                                5 => "FR", // Friday
-                                6 => "SA", // Saturday
-                                _ => return None,
+    // DEBUG: Log the recurrence field to see what we're receiving
+    println!("🔍 DEBUG: Received recurrence field: '{}'", request.recurrence);
+    println!("🔍 DEBUG: Starts with FREQ=? {}", request.recurrence.starts_with("FREQ="));
+    
+    // Check if recurrence is already a full RRULE or just a simple type
+    let rrule = if request.recurrence.starts_with("FREQ=") {
+        // Frontend sent a complete RRULE string, use it directly
+        println!("🎯 Using complete RRULE from frontend: {}", request.recurrence);
+        if request.recurrence.is_empty() {
+            None
+        } else {
+            Some(request.recurrence.clone())
+        }
+    } else {
+        // Legacy path: Parse recurrence with BYDAY support for weekly recurrence
+        println!("🔄 Building RRULE from simple recurrence type: {}", request.recurrence);
+        match request.recurrence.to_uppercase().as_str() {
+            "DAILY" => Some("FREQ=DAILY".to_string()),
+            "WEEKLY" => {
+                // Handle weekly recurrence with optional BYDAY parameter
+                let mut rrule = "FREQ=WEEKLY".to_string();
+                
+                // Check if specific days are selected (recurrence_days has 7 elements: [Sun, Mon, Tue, Wed, Thu, Fri, Sat])
+                if request.recurrence_days.len() == 7 {
+                    let selected_days: Vec<&str> = request.recurrence_days
+                        .iter()
+                        .enumerate()
+                        .filter_map(|(i, &selected)| {
+                            if selected {
+                                Some(match i {
+                                    0 => "SU", // Sunday
+                                    1 => "MO", // Monday
+                                    2 => "TU", // Tuesday
+                                    3 => "WE", // Wednesday
+                                    4 => "TH", // Thursday
+                                    5 => "FR", // Friday
+                                    6 => "SA", // Saturday
+                                    _ => return None,
                             })
                         } else {
                             None
@@ -419,11 +434,12 @@ pub async fn create_event(
                 }
             }
             
-            Some(rrule)
-        },
-        "MONTHLY" => Some("FREQ=MONTHLY".to_string()),
-        "YEARLY" => Some("FREQ=YEARLY".to_string()),
-        _ => None,
+                Some(rrule)
+            },
+            "MONTHLY" => Some("FREQ=MONTHLY".to_string()),
+            "YEARLY" => Some("FREQ=YEARLY".to_string()),
+            _ => None,
+        }
     };
 
     // Create the VEvent struct (RFC 5545 compliant)