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>

packages/db/src/schema/social.ts

@@ -11,7 +11,7 @@ import {
 } from "drizzle-orm/pg-core";
 import { relations } from "drizzle-orm";
 import { users } from "./users";
-import { recipes, recipeBatchDishes } from "./recipes";
+import { recipes, recipeBatchDishes, visibilityEnum } from "./recipes";
 
 export const notificationTypeEnum = pgEnum("notification_type", [
   "follow",
@@ -63,7 +63,7 @@ export const collections = pgTable("collections", {
   description: text("description"),
   notes: text("notes"),
   tags: text("tags").array().notNull().default([]),
-  isPublic: boolean("is_public").notNull().default(false),
+  visibility: visibilityEnum("visibility").notNull().default("private"),
   createdAt: timestamp("created_at").notNull().defaultNow(),
   updatedAt: timestamp("updated_at").notNull().defaultNow(),
 }, (t) => [