feat(domain): Add initial domain models for calendar, event, and recurrenceHEADmaster

- Added `calendar.rs` with Calendar entity and builder
- Added `event.rs` with Event model and builder
- Added `recurrence.rs` for recurrence rules
- Added `mod.rs` to expose domain module structure

These files establish the core domain layer structures
for future business logic.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/domain/mod.rs b/src/domain/mod.rs
new file mode 100644
index 0000000..f31bc30
--- /dev/null
+++ b/src/domain/mod.rs
@@ -0,0 +1,6 @@
+pub mod event;
+pub mod recurrence;
+pub mod calendar;
+
+pub use event::Event;
+pub use recurrence::{RecurrenceRule, Frequency};