Implement complete CalDAV events integration

Added full CalDAV integration to display real calendar events from Baikal server:

Backend changes:
- Added CalDAV client with iCalendar parsing and XML handling
- Created /api/calendar/events endpoint with authentication
- Fixed multiline regex patterns for namespace-prefixed XML tags
- Added proper calendar path discovery and event filtering

Frontend changes:
- Created CalendarService for API communication
- Updated calendar UI to display events as blue boxes with titles
- Added loading states and error handling
- Integrated real-time event fetching on calendar load

Now successfully displays 3 test events from the Baikal server with proper date formatting and responsive design.

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

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

backend/src/lib.rs

@@ -10,6 +10,8 @@ use std::sync::Arc;
 mod auth;
 mod models;
 mod handlers;
+mod calendar;
+mod config;
 
 use auth::AuthService;
 
@@ -50,6 +52,7 @@ pub async fn run_server() -> Result<(), Box<dyn std::error::Error>> {
         .route("/api/auth/register", post(handlers::register))
         .route("/api/auth/login", post(handlers::login))
         .route("/api/auth/verify", get(handlers::verify_token))
+        .route("/api/calendar/events", get(handlers::get_calendar_events))
         .layer(
             CorsLayer::new()
                 .allow_origin(Any)