feat: collections visibility enum (matches recipes) + QR on collection PDF (v0.54.0)

Replaces collections.isPublic (boolean) with collections.visibility
(private/unlisted/public/followers — same enum recipes use). Two-step
migration (0050 adds+backfills, 0051 drops isPublic) since drizzle-kit's
add+drop-in-one-diff rename heuristic needs an interactive prompt we
can't satisfy here.

New collectionVisibleToViewer(viewerId) in lib/visibility.ts mirrors the
existing recipe helper (author always sees own; public/unlisted visible
to anyone; followers-only via the same user_follows EXISTS pattern) —
used by the collection detail page, its print view, fork, and favorite,
replacing their old `or(isPublic, own)` checks.

Create/edit collection dialogs get the same 4-option visibility select
as the recipe form instead of a public/private checkbox.

Collection PDF export now generates a QR code (qrcode, same as the
recipe PDF) linking to /collections/{id}, shown only when visibility is
public/unlisted — same "would an anonymous scanner actually resolve
this" rule as the recipe QR.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/components/collections/collections-page-content.tsx

@@ -26,7 +26,7 @@ type Collection = {
   name: string;
   description: string | null;
   tags: string[];
-  isPublic: boolean;
+  visibility: "private" | "unlisted" | "public" | "followers";
   recipeCount: number;
   thumbnails: Thumbnail[];
 };
@@ -70,6 +70,7 @@ function CollectionThumbCollage({ thumbnails }: { thumbnails: Thumbnail[] }) {
 
 export function CollectionsPageContent({ collections, query }: Props) {
   const t = useTranslations("collections");
+  const tRecipe = useTranslations("recipe");
   const router = useRouter();
   const pathname = usePathname();
   const [search, setSearch] = useState(query);
@@ -129,7 +130,9 @@ export function CollectionsPageContent({ collections, query }: Props) {
               <div className="p-4 space-y-2">
                 <div className="flex items-start justify-between gap-2">
                   <h2 className="font-semibold group-hover:text-primary transition-colors line-clamp-1">{col.name}</h2>
-                  {col.isPublic && <Badge variant="secondary" className="text-xs shrink-0">{t("public")}</Badge>}
+                  {col.visibility !== "private" && (
+                    <Badge variant="secondary" className="text-xs shrink-0">{tRecipe(`visibility.${col.visibility}`)}</Badge>
+                  )}
                 </div>
                 {col.description && <p className="text-sm text-muted-foreground line-clamp-2">{col.description}</p>}
                 {col.tags.length > 0 && (