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.

Cargo.toml

@@ -25,6 +25,9 @@ reqwest = { version = "0.11", features = ["json", "rustls-tls"] }
 # iCalendar parsing
 icalendar = "0.15"
 
+# RRULE recurrence processing
+rrule = { version = "0.14", features = ["serde"] }
+
 # Serialization
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
@@ -62,6 +65,9 @@ url = "2.3"
 # TOML parsing
 toml = "0.8"
 
+# MD5 hashing for unique identifier generation
+md5 = "0.7"
+
 [dev-dependencies]
 tokio-test = "0.4"
 tempfile = "3.0"