Replace page reloads with dynamic calendar refresh functionality

- Add refresh_calendar_data function to replace window.location.reload()
- Implement dynamic event re-fetching without full page refresh
- Add last_updated timestamp to UserInfo to force component re-renders
- Fix WASM compatibility by using js_sys::Date::now() instead of SystemTime
- Remove debug logging from refresh operations
- Maintain same user experience with improved performance

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

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

frontend/Cargo.toml

@@ -30,6 +30,7 @@ web-sys = { version = "0.3", features = [
     "CssStyleDeclaration",
 ] }
 wasm-bindgen = "0.2"
+js-sys = "0.3"
 
 # HTTP client for CalDAV requests
 reqwest = { version = "0.11", features = ["json"] }