Complete event modal migration: remove original and rename V2

Remove the original create_event_modal.rs and rename create_event_modal_v2.rs
to complete the modal migration started earlier. This eliminates duplicate code
and consolidates to a single, clean event modal implementation.

Changes:
- Remove original create_event_modal.rs (2,300+ lines)
- Rename create_event_modal_v2.rs → create_event_modal.rs
- Update component/function names: CreateEventModalV2 → CreateEventModal
- Fix all imports in app.rs and calendar.rs
- Add missing to_create_event_params() method to EventCreationData
- Resolve EditAction type conflicts between modules
- Clean up duplicate types and unused imports
- Maintain backwards compatibility with EventCreationData export

Result: -2440 lines, +160 lines - massive code cleanup with zero functionality loss.

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

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

frontend/src/components/event_form/reminders.rs

@@ -1,5 +1,5 @@
 use super::types::*;
-use crate::components::create_event_modal::ReminderType;
+// Types are already imported from super::types::*
 use wasm_bindgen::JsCast;
 use web_sys::HtmlSelectElement;
 use yew::prelude::*;