Remove v2 API endpoints and fix warnings

- Remove all v2 API routes (/api/v2/calendar/events/*)
- Delete models_v2.rs file and associated types
- Remove create_event_v2, update_event_v2, delete_event_v2 handlers
- Remove unused occurrence_date and exception_dates from UpdateEventRequest
- Remove unused ConfigError variant from CalDAVError
- Simplify backend to single unified v1 API using VEvent structures

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

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

backend/src/lib.rs

@@ -8,7 +8,6 @@ use std::sync::Arc;
 
 mod auth;
 mod models;
-mod models_v2;
 mod handlers;
 mod calendar;
 mod config;
@@ -45,10 +44,6 @@ pub async fn run_server() -> Result<(), Box<dyn std::error::Error>> {
         .route("/api/calendar/events/create", post(handlers::create_event))
         .route("/api/calendar/events/update", post(handlers::update_event))
         .route("/api/calendar/events/delete", post(handlers::delete_event))
-        // V2 API routes with better type safety
-        .route("/api/v2/calendar/events/create", post(handlers::create_event_v2))
-        .route("/api/v2/calendar/events/update", post(handlers::update_event_v2))
-        .route("/api/v2/calendar/events/delete", post(handlers::delete_event_v2))
         .route("/api/calendar/events/:uid", get(handlers::refresh_event))
         .layer(
             CorsLayer::new()