Implement complete calendar creation functionality

Add full end-to-end calendar creation feature including:
- Create Calendar button in sidebar footer
- Modal form with name, description, and color picker (16 predefined colors in 4x4 grid)
- Form validation and error handling with loading states
- Backend API endpoint for calendar creation with authentication
- CalDAV MKCALENDAR protocol implementation with proper XML generation
- Real-time calendar list refresh after successful creation
- Responsive design for mobile and desktop

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

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

backend/src/handlers.rs

@@ -7,7 +7,7 @@ use serde::Deserialize;
 use std::sync::Arc;
 use chrono::Datelike;
 
-use crate::{AppState, models::{CalDAVLoginRequest, AuthResponse, ApiError, UserInfo, CalendarInfo}};
+use crate::{AppState, models::{CalDAVLoginRequest, AuthResponse, ApiError, UserInfo, CalendarInfo, CreateCalendarRequest, CreateCalendarResponse}};
 use crate::calendar::{CalDAVClient, CalendarEvent};
 
 #[derive(Deserialize)]
@@ -252,4 +252,44 @@ fn extract_password_header(headers: &HeaderMap) -> Result<String, ApiError> {
     } else {
         Err(ApiError::BadRequest("X-CalDAV-Password header required".to_string()))
     }
+}
+
+pub async fn create_calendar(
+    State(state): State<Arc<AppState>>,
+    headers: HeaderMap,
+    Json(request): Json<CreateCalendarRequest>,
+) -> Result<Json<CreateCalendarResponse>, ApiError> {
+    println!("📝 Create calendar request received: name='{}', description={:?}, color={:?}", 
+             request.name, request.description, request.color);
+    
+    // Extract and verify token
+    let token = extract_bearer_token(&headers)?;
+    let password = extract_password_header(&headers)?;
+
+    // Validate request
+    if request.name.trim().is_empty() {
+        return Err(ApiError::BadRequest("Calendar name is required".to_string()));
+    }
+    
+    if request.name.len() > 100 {
+        return Err(ApiError::BadRequest("Calendar name too long (max 100 characters)".to_string()));
+    }
+
+    // Create CalDAV config from token and password
+    let config = state.auth_service.caldav_config_from_token(&token, &password)?;
+    let client = CalDAVClient::new(config);
+
+    // Create the calendar
+    client.create_calendar(
+        &request.name,
+        request.description.as_deref(),
+        request.color.as_deref()
+    )
+    .await
+    .map_err(|e| ApiError::Internal(format!("Failed to create calendar: {}", e)))?;
+
+    Ok(Json(CreateCalendarResponse {
+        success: true,
+        message: "Calendar created successfully".to_string(),
+    }))
 }