fix: Handle updatedAt as string in admin form autosave

Fixed TypeError when updatedAt field from JSON responses was incorrectly
treated as Date object. Added type guards to handle both string and Date
types in autosave callbacks across all admin forms.

src/lib/components/admin/AlbumForm.svelte

@@ -46,7 +46,13 @@
 	let editorInstance = $state<{ save: () => Promise<JSONContent>; clear: () => void } | undefined>()
 	let activeTab = $state('metadata')
 	let pendingMediaIds = $state<number[]>([]) // Photos to add after album creation
-	let updatedAt = $state<string | undefined>(album?.updatedAt?.toISOString())
+	let updatedAt = $state<string | undefined>(
+		album?.updatedAt
+			? typeof album.updatedAt === 'string'
+				? album.updatedAt
+				: album.updatedAt.toISOString()
+			: undefined
+	)
 
 	const tabOptions = [
 		{ value: 'metadata', label: 'Metadata' },
@@ -114,7 +120,8 @@
 					return await response.json()
 				},
 				onSaved: (saved: Album, { prime }) => {
-					updatedAt = saved.updatedAt.toISOString()
+					updatedAt =
+						typeof saved.updatedAt === 'string' ? saved.updatedAt : saved.updatedAt.toISOString()
 					prime(buildPayload())
 					if (draftKey) clearDraft(draftKey)
 				}

src/lib/components/admin/EssayForm.svelte

@@ -79,7 +79,8 @@
 					return await response.json()
 				},
 				onSaved: (saved: Post, { prime }) => {
-					updatedAt = saved.updatedAt.toISOString()
+					updatedAt =
+					typeof saved.updatedAt === 'string' ? saved.updatedAt : saved.updatedAt.toISOString()
 					prime(buildPayload())
 					if (draftKey) clearDraft(draftKey)
 				}

src/lib/components/admin/PhotoPostForm.svelte

@@ -97,7 +97,8 @@ let autoSave = mode === 'edit' && postId
 				return await response.json()
 			},
 			onSaved: (saved: Post, { prime }) => {
-				updatedAt = saved.updatedAt.toISOString()
+				updatedAt =
+				typeof saved.updatedAt === 'string' ? saved.updatedAt : saved.updatedAt.toISOString()
 				prime(buildPayload())
 				if (draftKey) clearDraft(draftKey)
 			}

src/lib/components/admin/SimplePostForm.svelte

@@ -115,7 +115,8 @@ let autoSave = mode === 'edit' && postId
 				return await response.json()
 			},
 			onSaved: (saved: Post, { prime }) => {
-				updatedAt = saved.updatedAt.toISOString()
+				updatedAt =
+				typeof saved.updatedAt === 'string' ? saved.updatedAt : saved.updatedAt.toISOString()
 				prime(buildPayload())
 				if (draftKey) clearDraft(draftKey)
 			}