feat: Complete import functionality with RRULE fixes and comprehensive testing

- Fix RRULE BYDAY filtering for daily frequency events (Tether sync weekdays only)
- Fix timezone transfer in recurring event expansion
- Add comprehensive timezone-aware iCal generation
- Add extensive test suite for recurrence and timezone functionality
- Update dependencies and configuration examples
- Implement cleanup logic for orphaned events
- Add detailed import plan documentation

This completes the core import functionality with proper timezone handling,
RRULE parsing, and duplicate prevention mechanisms.

test_timezone.rs

@@ -0,0 +1,22 @@
+use chrono::{DateTime, Utc, NaiveDateTime};
+
+fn main() {
+    let start = DateTime::from_naive_utc_and_offset(
+        NaiveDateTime::parse_from_str("20231225T083000", "%Y%m%dT%H%M%S").unwrap(),
+        Utc
+    );
+    let end = start + chrono::Duration::minutes(30);
+    
+    let mut event = caldav_sync::event::Event::new("Tether Sync".to_string(), start, end);
+    event.timezone = Some("America/Toronto".to_string());
+    
+    let ical = event.to_ical().unwrap();
+    println!("=== Event with Timezone (America/Toronto) ===");
+    println!("{}", ical);
+    println!("\n");
+    
+    let utc_event = caldav_sync::event::Event::new("UTC Event".to_string(), start, end);
+    let ical_utc = utc_event.to_ical().unwrap();
+    println!("=== Event without Timezone (fallback to UTC) ===");
+    println!("{}", ical_utc);
+}