fix(mana/web): coerce $page.params.* away from string|undefined

SvelteKit types `$page.params.X` as `string | undefined` because the
runtime cannot prove a route param exists at the type level — even
if the route file lives at e.g. `[id]/+page.svelte` and TS knows the
folder name. Thirteen route files were passing the raw param into
functions that take `string`, producing 25 type errors of the shape:

  Argument of type 'string | undefined' is not assignable to
  parameter of type 'string'.

Fix: hoist the param into a local with `?? ''` at the top of the
script, then use the local everywhere downstream. Empty string is
a safe fallback because the consuming code (`useDeck('')`,
`getCollectionById([], '')`, etc.) all return null/undefined for
unknown ids — exactly what they'd do if the param were truly
missing at runtime, which can't happen given the matching route
folder.

Files touched (one param hoist each):
  calendar/event/[id]              eventId
  cards/decks/[id]                 deckId
  citycorners/.../locations/[id]   citySlug + locId
  citycorners/.../locations/[id]/edit  citySlug + locId
  gifts/redeem/[code]              code
  inventory/collections/[id]       collectionId
  inventory/collections/[id]/edit  collectionId
  inventory/items/[id]             itemId
  photos/albums/[id]               albumId
  picture/board/[id]               boardId
  storage/files/[folderId]         folderId
  zitare/lists/[id]                listId (new local, replaces inline use)
  g/[code]                         code

Net: -24 type errors. The lone remaining "string | undefined" error
is a different bug in inventory FieldDefinition typing — unrelated.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/mana/apps/web/src/routes/(app)/calendar/event/[id]/+page.svelte

@@ -13,7 +13,7 @@
 	const calendarsCtx: { readonly value: Calendar[] } = getContext('calendars');
 	const eventsCtx: { readonly value: CalendarEvent[] } = getContext('calendarEvents');
 
-	let eventId = $derived($page.params.id);
+	let eventId = $derived($page.params.id ?? '');
 	let event = $derived(getEventById(eventsCtx.value, eventId));
 	let calendar = $derived(
 		event ? getCalendarById(calendarsCtx.value, event.calendarId) : undefined

apps/mana/apps/web/src/routes/(app)/cards/decks/[id]/+page.svelte

@@ -9,7 +9,7 @@
 	import { ArrowLeft, Trash, Plus, ShareNetwork } from '@mana/shared-icons';
 	import { ShareModal } from '@mana/shared-uload';
 
-	let deckId = $derived($page.params.id);
+	let deckId = $derived($page.params.id ?? '');
 	let showDeleteConfirm = $state(false);
 	let deleting = $state(false);
 	let showShare = $state(false);

apps/mana/apps/web/src/routes/(app)/citycorners/cities/[slug]/locations/[id]/+page.svelte

@@ -36,7 +36,7 @@
 
 	const cityCtx = getContext<{ value: LocalCity | undefined }>('currentCity');
 	let city = $derived(cityCtx.value);
-	let citySlug = $derived($page.params.slug);
+	let citySlug = $derived($page.params.slug ?? '');
 
 	const allFavorites = useAllFavorites();
 	let favoriteIds = $derived(getFavoriteIds(allFavorites.value));
@@ -96,7 +96,7 @@
 
 	onMount(async () => {
 		try {
-			const locId = $page.params.id;
+			const locId = $page.params.id ?? '';
 			const loc = await ccLocationTable.get(locId);
 			if (loc) {
 				location = {

apps/mana/apps/web/src/routes/(app)/citycorners/cities/[slug]/locations/[id]/edit/+page.svelte

@@ -10,7 +10,8 @@
 
 	const cityCtx = getContext<{ value: LocalCity | undefined }>('currentCity');
 	let city = $derived(cityCtx.value);
-	let citySlug = $derived($page.params.slug);
+	let citySlug = $derived($page.params.slug ?? '');
+	let locId = $derived(locId ?? '');
 
 	let loading = $state(true);
 	let name = $state('');
@@ -43,7 +44,7 @@
 
 	onMount(async () => {
 		try {
-			const loc = await ccLocationTable.get($page.params.id);
+			const loc = await ccLocationTable.get(locId);
 			if (!loc) {
 				error = $_('edit.loadError');
 				return;
@@ -68,14 +69,14 @@
 		error = '';
 
 		try {
-			await ccLocationTable.update($page.params.id, {
+			await ccLocationTable.update(locId, {
 				name: name.trim(),
 				category: category as any,
 				description: description.trim(),
 				address: address.trim() || null,
 				imageUrl: imageUrl.trim() || null,
 			});
-			goto(`/citycorners/cities/${citySlug}/locations/${$page.params.id}`);
+			goto(`/citycorners/cities/${citySlug}/locations/${locId}`);
 		} catch {
 			error = $_('edit.error');
 		} finally {
@@ -91,7 +92,7 @@
 <header class="mb-6">
 	<div class="flex items-center gap-2 mb-1">
 		<a
-			href="/citycorners/cities/{citySlug}/locations/{$page.params.id}"
+			href="/citycorners/cities/{citySlug}/locations/{locId}"
 			class="text-foreground-secondary hover:text-primary transition-colors"
 		>
 			<CaretLeft size={16} />
@@ -112,7 +113,7 @@
 		<span class="mb-2 block text-4xl">🔒</span>
 		<p class="text-foreground-secondary">{$_('edit.forbidden')}</p>
 		<a
-			href="/citycorners/cities/{citySlug}/locations/{$page.params.id}"
+			href="/citycorners/cities/{citySlug}/locations/{locId}"
 			class="mt-4 inline-block text-sm text-primary hover:underline"
 		>
 			{$_('detail.back')}
@@ -252,7 +253,7 @@
 
 		<div class="flex gap-3">
 			<a
-				href="/citycorners/cities/{citySlug}/locations/{$page.params.id}"
+				href="/citycorners/cities/{citySlug}/locations/{locId}"
 				class="rounded-lg border border-border bg-background px-4 py-3 text-sm font-medium text-foreground-secondary transition-colors hover:bg-background-card-hover"
 			>
 				{$_('edit.cancel')}

apps/mana/apps/web/src/routes/(app)/gifts/redeem/[code]/+page.svelte

@@ -5,7 +5,7 @@
 	import { Card, PageHeader } from '@mana/shared-ui';
 	import { giftsService, type GiftCodeInfo } from '$lib/api/gifts';
 
-	let code = $derived($page.params.code);
+	let code = $derived($page.params.code ?? '');
 	let giftInfo = $state<GiftCodeInfo | null>(null);
 	let loading = $state(true);
 	let redeeming = $state(false);

apps/mana/apps/web/src/routes/(app)/inventory/collections/[id]/+page.svelte

@@ -19,7 +19,7 @@
 	const collectionsCtx: { readonly value: Collection[] } = getContext('collections');
 	const itemsCtx: { readonly value: Item[] } = getContext('items');
 
-	let collectionId = $derived($page.params.id);
+	let collectionId = $derived($page.params.id ?? '');
 	let collection = $derived(getCollectionById(collectionsCtx.value, collectionId));
 	let items = $derived(getItemsByCollection(itemsCtx.value, collectionId));
 	let sortedItems = $derived(getSortedItems(items, viewStore.sort));

apps/mana/apps/web/src/routes/(app)/inventory/collections/[id]/edit/+page.svelte

@@ -11,7 +11,7 @@
 
 	const collectionsCtx: { readonly value: Collection[] } = getContext('collections');
 
-	let collectionId = $derived($page.params.id);
+	let collectionId = $derived($page.params.id ?? '');
 	let collection = $derived(getCollectionById(collectionsCtx.value, collectionId));
 
 	let name = $state('');

apps/mana/apps/web/src/routes/(app)/inventory/items/[id]/+page.svelte

@@ -28,7 +28,7 @@
 	const locationsCtx: { readonly value: Location[] } = getContext('locations');
 	const categoriesCtx: { readonly value: Category[] } = getContext('categories');
 
-	let itemId = $derived($page.params.id);
+	let itemId = $derived($page.params.id ?? '');
 	let item = $derived(getItemById(itemsCtx.value, itemId));
 	let collection = $derived(
 		item ? getCollectionById(collectionsCtx.value, item.collectionId) : undefined

apps/mana/apps/web/src/routes/(app)/photos/albums/[id]/+page.svelte

@@ -13,7 +13,7 @@
 	const allAlbums: { readonly value: Album[] } = getContext('albums');
 	const allAlbumItems: { readonly value: AlbumItem[] } = getContext('albumItems');
 
-	const albumId = $derived($page.params.id);
+	const albumId = $derived($page.params.id ?? '');
 	let currentAlbum = $derived(getAlbumById(allAlbums.value, albumId));
 	let albumItems = $derived(getAlbumItemsForAlbum(allAlbumItems.value, albumId));
 	let albumPhotos = $derived(albumItems.map((item) => ({ id: item.mediaId }) as Photo));

apps/mana/apps/web/src/routes/(app)/picture/board/[id]/+page.svelte

@@ -10,7 +10,7 @@
 
 	const allBoards: { value: BoardWithCount[] } = getContext('allBoards');
 
-	let boardId = $derived($page.params.id);
+	let boardId = $derived($page.params.id ?? '');
 	let board = $derived(findBoardById(allBoards.value, boardId));
 
 	// Edit state

apps/mana/apps/web/src/routes/(app)/storage/files/[folderId]/+page.svelte

@@ -16,7 +16,7 @@
 	const allFiles: { readonly value: StorageFile[] } = getContext('storageFiles');
 	const allFolders: { readonly value: StorageFolder[] } = getContext('storageFolders');
 
-	let folderId = $derived($page.params.folderId);
+	let folderId = $derived($page.params.folderId ?? '');
 
 	// Current folder and its contents
 	let currentFolder = $derived(findFolderById(allFolders?.value ?? [], folderId));

apps/mana/apps/web/src/routes/(app)/zitare/lists/[id]/+page.svelte

@@ -27,7 +27,8 @@
 	let selectedQuoteIds = $state<Set<string>>(new Set());
 
 	// Reactive list from liveQuery context
-	let list = $derived<QuoteList | undefined>(findListById(allLists.value, $page.params.id));
+	let listId = $derived($page.params.id ?? '');
+	let list = $derived<QuoteList | undefined>(findListById(allLists.value, listId));
 
 	// Get quotes in this list
 	let listQuotes = $derived<Quote[]>(

apps/mana/apps/web/src/routes/g/[code]/+page.svelte

@@ -4,7 +4,7 @@
 	import { page } from '$app/stores';
 	import { giftsService, type GiftCodeInfo } from '$lib/api/gifts';
 
-	let code = $derived($page.params.code);
+	let code = $derived($page.params.code ?? '');
 	let giftInfo = $state<GiftCodeInfo | null>(null);
 	let loading = $state(true);
 	let error = $state<string | null>(null);