Implement event deletion with right-click context menu

- Add EventContextMenu component with delete option
- Create DELETE /api/calendar/events/delete endpoint
- Implement CalDAV event deletion in backend
- Add proper URL construction for CalDAV event hrefs
- Integrate context menu with calendar event right-clicks
- Auto-refresh UI after successful event deletion

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

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

src/components/event_context_menu.rs

@@ -0,0 +1,47 @@
+use yew::prelude::*;
+use web_sys::MouseEvent;
+
+#[derive(Properties, PartialEq)]
+pub struct EventContextMenuProps {
+    pub is_open: bool,
+    pub x: i32,
+    pub y: i32,
+    pub on_delete: Callback<MouseEvent>,
+    pub on_close: Callback<()>,
+}
+
+#[function_component(EventContextMenu)]
+pub fn event_context_menu(props: &EventContextMenuProps) -> Html {
+    let menu_ref = use_node_ref();
+    
+    if !props.is_open {
+        return html! {};
+    }
+
+    let style = format!(
+        "position: fixed; left: {}px; top: {}px; z-index: 1001;",
+        props.x, props.y
+    );
+
+    let on_delete_click = {
+        let on_delete = props.on_delete.clone();
+        let on_close = props.on_close.clone();
+        Callback::from(move |e: MouseEvent| {
+            on_delete.emit(e);
+            on_close.emit(());
+        })
+    };
+
+    html! {
+        <div 
+            ref={menu_ref}
+            class="context-menu" 
+            style={style}
+        >
+            <div class="context-menu-item context-menu-delete" onclick={on_delete_click}>
+                <span class="context-menu-icon">{"🗑️"}</span>
+                {"Delete Event"}
+            </div>
+        </div>
+    }
+}