Add clear day option to calendar

- Add clearDayData function to remove specific day's usage
- Add "Clear This Day" button in calendar edit dialog
- Allows users to reset individual days without clearing all data

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/UsageCalendar.tsx

@@ -12,7 +12,7 @@ import {
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';
-import { UsageEntry, getUsageForDate, setUsageForDate } from '@/lib/storage';
+import { UsageEntry, getUsageForDate, setUsageForDate, clearDayData } from '@/lib/storage';
 import { ChevronLeftIcon, ChevronRightIcon } from 'lucide-react';
 
 interface UsageCalendarProps {
@@ -59,6 +59,17 @@ export function UsageCalendar({ usageData, substance, onDataUpdate }: UsageCalen
     setEditCount('');
   };
 
+  const handleClearDay = () => {
+    if (selectedDate) {
+      const dateStr = selectedDate.toISOString().split('T')[0];
+      clearDayData(dateStr, substance);
+      onDataUpdate();
+    }
+    setIsEditing(false);
+    setSelectedDate(undefined);
+    setEditCount('');
+  };
+
   const getUsageCount = useCallback((date: Date): number => {
     const dateStr = date.toISOString().split('T')[0];
     const entry = usageData.find((e) => e.date === dateStr && e.substance === substance);
@@ -179,6 +190,15 @@ export function UsageCalendar({ usageData, substance, onDataUpdate }: UsageCalen
                 Save
               </Button>
             </div>
+            <div className="pt-2 border-t">
+              <Button
+                variant="destructive"
+                onClick={handleClearDay}
+                className="w-full"
+              >
+                Clear This Day
+              </Button>
+            </div>
           </div>
         </DialogContent>
       </Dialog>

src/lib/storage.ts

@@ -191,6 +191,13 @@ export function getCurrentWeekTarget(): number | null {
   return prefs.quitPlan.weeklyTargets[weekNumber];
 }
 
+export function clearDayData(date: string, substance: 'nicotine' | 'weed'): void {
+  if (typeof window === 'undefined') return;
+  const data = getUsageData();
+  const filtered = data.filter((e) => !(e.date === date && e.substance === substance));
+  localStorage.setItem(USAGE_KEY, JSON.stringify(filtered));
+}
+
 export function clearAllData(): void {
   if (typeof window === 'undefined') return;
   localStorage.removeItem(USAGE_KEY);