Fix calendar event fetching to use visible date range

Moved event fetching logic from CalendarView to Calendar component to properly
use the visible date range instead of hardcoded current month. The Calendar
component already tracks the current visible date through navigation, so events
now load correctly for August and other months when navigating.

Changes:
- Calendar component now manages its own events state and fetching
- Event fetching responds to current_date changes from navigation
- CalendarView simplified to just render Calendar component
- Fixed cargo fmt/clippy formatting across codebase

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

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

backend/src/handlers.rs

@@ -4,7 +4,7 @@ mod calendar;
 mod events;
 mod series;
 
-pub use auth::{login, verify_token, get_user_info};
+pub use auth::{get_user_info, login, verify_token};
 pub use calendar::{create_calendar, delete_calendar};
-pub use events::{get_calendar_events, refresh_event, create_event, update_event, delete_event};
-pub use series::{create_event_series, update_event_series, delete_event_series};
+pub use events::{create_event, delete_event, get_calendar_events, refresh_event, update_event};
+pub use series::{create_event_series, delete_event_series, update_event_series};