Replace native date/time inputs with DatePicker across calendar and todo forms

- EventForm + EventDetailPanel: native <Input type=date|datetime-local> → DatePicker with dynamic mode via all_day toggle
- TodoForm + TodoDetailPanel: merge date + time into single datetime DatePicker, remove separate time input, move recurrence select into 2-col grid beside date picker

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/calendar/EventDetailPanel.tsx

@@ -13,6 +13,7 @@ import { formatUpdatedAt } from '@/components/shared/utils';
 import CopyableField from '@/components/shared/CopyableField';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
+import { DatePicker } from '@/components/ui/date-picker';
 import { Textarea } from '@/components/ui/textarea';
 import { Select } from '@/components/ui/select';
 import { Checkbox } from '@/components/ui/checkbox';
@@ -633,22 +634,24 @@ export default function EventDetailPanel({
             <div className="grid grid-cols-2 gap-3">
               <div className="space-y-1">
                 <Label htmlFor="panel-start" required>Start</Label>
-                <Input
+                <DatePicker
+                  variant="input"
                   id="panel-start"
-                  type={editState.all_day ? 'date' : 'datetime-local'}
+                  mode={editState.all_day ? 'date' : 'datetime'}
                   value={editState.start_datetime}
-                  onChange={(e) => updateField('start_datetime', e.target.value)}
+                  onChange={(v) => updateField('start_datetime', v)}
                   className="text-xs"
                   required
                 />
               </div>
               <div className="space-y-1">
                 <Label htmlFor="panel-end">End</Label>
-                <Input
+                <DatePicker
+                  variant="input"
                   id="panel-end"
-                  type={editState.all_day ? 'date' : 'datetime-local'}
+                  mode={editState.all_day ? 'date' : 'datetime'}
                   value={editState.end_datetime}
-                  onChange={(e) => updateField('end_datetime', e.target.value)}
+                  onChange={(v) => updateField('end_datetime', v)}
                   className="text-xs"
                 />
               </div>

frontend/src/components/calendar/EventForm.tsx

@@ -13,6 +13,7 @@ import {
   SheetClose,
 } from '@/components/ui/sheet';
 import { Input } from '@/components/ui/input';
+import { DatePicker } from '@/components/ui/date-picker';
 import { Textarea } from '@/components/ui/textarea';
 import { Select } from '@/components/ui/select';
 import { Label } from '@/components/ui/label';
@@ -281,22 +282,24 @@ export default function EventForm({ event, templateData, templateName, initialSt
             <div className="grid grid-cols-2 gap-4">
               <div className="space-y-2">
                 <Label htmlFor="start" required>Start</Label>
-                <Input
+                <DatePicker
+                  variant="input"
                   id="start"
-                  type={formData.all_day ? 'date' : 'datetime-local'}
+                  mode={formData.all_day ? 'date' : 'datetime'}
                   value={formData.start_datetime}
-                  onChange={(e) => setFormData({ ...formData, start_datetime: e.target.value })}
+                  onChange={(v) => setFormData({ ...formData, start_datetime: v })}
                   required
                 />
               </div>
 
               <div className="space-y-2">
                 <Label htmlFor="end">End</Label>
-                <Input
+                <DatePicker
+                  variant="input"
                   id="end"
-                  type={formData.all_day ? 'date' : 'datetime-local'}
+                  mode={formData.all_day ? 'date' : 'datetime'}
                   value={formData.end_datetime}
-                  onChange={(e) => setFormData({ ...formData, end_datetime: e.target.value })}
+                  onChange={(v) => setFormData({ ...formData, end_datetime: v })}
                 />
               </div>
             </div>

frontend/src/components/todos/TodoDetailPanel.tsx

@@ -389,23 +389,15 @@ export default function TodoDetailPanel({
                 <DatePicker
                   variant="input"
                   id="todo-due-date"
-                  value={editState.due_date}
+                  mode="datetime"
-                  onChange={(v) => updateField('due_date', v)}
+                  value={editState.due_date ? (editState.due_date + 'T' + (editState.due_time || '00:00')) : ''}
+                  onChange={(v) => {
+                    updateField('due_date', v ? v.slice(0, 10) : '');
+                    updateField('due_time', v ? v.slice(11, 16) : '');
+                  }}
                   className="text-xs"
                 />
               </div>
-              <div className="space-y-1">
-                <Label htmlFor="todo-due-time">Due Time</Label>
-                <Input
-                  id="todo-due-time"
-                  type="time"
-                  value={editState.due_time}
-                  onChange={(e) => updateField('due_time', e.target.value)}
-                  className="text-xs"
-                />
-              </div>
-            </div>
-
               <div className="space-y-1">
                 <Label htmlFor="todo-recurrence">Recurrence</Label>
                 <Select
@@ -420,6 +412,7 @@ export default function TodoDetailPanel({
                   <option value="monthly">Monthly</option>
                 </Select>
               </div>
+            </div>
 
             {/* Save / Cancel at bottom */}
             <div className="flex items-center justify-end gap-2 pt-2 border-t border-border">

frontend/src/components/todos/TodoForm.tsx

@@ -133,22 +133,16 @@ export default function TodoForm({ todo, onClose }: TodoFormProps) {
                 <DatePicker
                   variant="input"
                   id="due_date"
-                  value={formData.due_date}
+                  mode="datetime"
-                  onChange={(v) => setFormData({ ...formData, due_date: v })}
+                  value={formData.due_date ? (formData.due_date + 'T' + (formData.due_time || '00:00')) : ''}
+                  onChange={(v) => setFormData({
+                    ...formData,
+                    due_date: v ? v.slice(0, 10) : '',
+                    due_time: v ? v.slice(11, 16) : '',
+                  })}
                 />
               </div>
 
-              <div className="space-y-2">
-                <Label htmlFor="due_time">Due Time</Label>
-                <Input
-                  id="due_time"
-                  type="time"
-                  value={formData.due_time}
-                  onChange={(e) => setFormData({ ...formData, due_time: e.target.value })}
-                />
-              </div>
-            </div>
-
               <div className="space-y-2">
                 <Label htmlFor="recurrence">Recurrence</Label>
                 <Select
@@ -163,6 +157,7 @@ export default function TodoForm({ todo, onClose }: TodoFormProps) {
                 </Select>
               </div>
             </div>
+          </div>
 
           <SheetFooter>
             <Button type="button" variant="outline" onClick={onClose}>