Add configurable time increment toggle for event creation

- Add toggle button (15/30 minutes) in calendar header next to navigation arrows
- Implement circular frosted styling consistent with nav buttons
- Add configurable snapping for drag-to-create events in week view
- Persist time increment setting across browser sessions using localStorage
- Update snap function to accept configurable increment instead of hardcoded 15 minutes

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

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

src/components/calendar.rs

@@ -66,6 +66,20 @@ pub fn Calendar(props: &CalendarProps) -> Html {
     let show_create_modal = use_state(|| false);
     let create_event_data = use_state(|| None::<(chrono::NaiveDate, chrono::NaiveTime, chrono::NaiveTime)>);
     
+    // State for time increment snapping (15 or 30 minutes)
+    let time_increment = use_state(|| {
+        // Try to load saved time increment from localStorage
+        if let Ok(saved_increment) = LocalStorage::get::<u32>("calendar_time_increment") {
+            if saved_increment == 15 || saved_increment == 30 {
+                saved_increment
+            } else {
+                15
+            }
+        } else {
+            15
+        }
+    });
+    
     // Handle view mode changes - adjust current_date format when switching between month/week
     {
         let current_date = current_date.clone();
@@ -152,6 +166,17 @@ pub fn Calendar(props: &CalendarProps) -> Html {
         })
     };
     
+    // Handle time increment toggle
+    let on_time_increment_toggle = {
+        let time_increment = time_increment.clone();
+        Callback::from(move |_: MouseEvent| {
+            let current = *time_increment;
+            let next = if current == 15 { 30 } else { 15 };
+            time_increment.set(next);
+            let _ = LocalStorage::set("calendar_time_increment", next);
+        })
+    };
+    
     // Handle drag-to-create event
     let on_create_event = {
         let show_create_modal = show_create_modal.clone();
@@ -172,6 +197,8 @@ pub fn Calendar(props: &CalendarProps) -> Html {
                 on_prev={on_prev}
                 on_next={on_next}
                 on_today={on_today}
+                time_increment={Some(*time_increment)}
+                on_time_increment_toggle={Some(on_time_increment_toggle)}
             />
             
             {
@@ -212,6 +239,7 @@ pub fn Calendar(props: &CalendarProps) -> Html {
                             on_calendar_context_menu={props.on_calendar_context_menu.clone()}
                             on_create_event={Some(on_create_event)}
                             context_menus_open={props.context_menus_open}
+                            time_increment={*time_increment}
                         />
                     },
                 }