Fix create-mode crash in detail panels (null entity access)

The desktop detail panels are pre-mounted (always in DOM, hidden with w-0).
useState(isCreating) only captures the initial value on mount (false), so
when isCreating later becomes true via props, isEditing stays false. The
view-mode branch then runs with a null entity, crashing on property access.

Fix: use (isEditing || isCreating) for all conditionals that gate between
edit/create form and view mode, ensuring the form always renders when
isCreating is true regardless of isEditing state.

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

frontend/src/components/calendar/EventDetailPanel.tsx

@@ -480,7 +480,7 @@ export default function EventDetailPanel({
               >
                 <X className="h-3.5 w-3.5" />
               </Button>
-            ) : isEditing ? (
+            ) : (isEditing || isCreating) ? (
               <>
                 <Button
                   variant="ghost"
@@ -586,7 +586,7 @@ export default function EventDetailPanel({
               </Button>
             </div>
           </div>
-        ) : isEditing ? (
+        ) : (isEditing || isCreating) ? (
           /* Edit / Create mode */
           <div className="space-y-4">
             {/* Title (only shown in body for create mode; edit mode has it in header) */}

frontend/src/components/reminders/ReminderDetailPanel.tsx

@@ -224,7 +224,7 @@ export default function ReminderDetailPanel({
           )}
 
           <div className="flex items-center gap-1 shrink-0">
-            {isEditing ? (
+            {(isEditing || isCreating) ? (
               <>
                 <Button
                   variant="ghost"
@@ -308,7 +308,7 @@ export default function ReminderDetailPanel({
 
       {/* Body */}
       <div className="flex-1 overflow-y-auto px-5 py-4 space-y-3">
-        {isEditing ? (
+        {(isEditing || isCreating) ? (
           /* Edit / Create mode */
           <div className="space-y-4">
             {isCreating && (

frontend/src/components/todos/TodoDetailPanel.tsx

@@ -254,7 +254,7 @@ export default function TodoDetailPanel({
           )}
 
           <div className="flex items-center gap-1 shrink-0">
-            {isEditing ? (
+            {(isEditing || isCreating) ? (
               <>
                 <Button
                   variant="ghost"
@@ -326,7 +326,7 @@ export default function TodoDetailPanel({
 
       {/* Body */}
       <div className="flex-1 overflow-y-auto px-5 py-4 space-y-3">
-        {isEditing ? (
+        {(isEditing || isCreating) ? (
           /* Edit / Create mode */
           <div className="space-y-4">
             {isCreating && (