feat: anonymous read-only public link + QR code for meal plans (v0.68.0)

Mirrors shopping lists' isPublic pattern but read-only only -- no
publicEditable equivalent, since anonymous editing of someone's
weekly meal schedule isn't a real use case the way collaborative
shopping-list editing is. New PATCH /api/v1/meal-plans/{weekStart}
toggles it (lazily creates the week's plan row if missing, same
pattern as the existing POST). Public page at /m/[id] renders the
week grouped by day, linking through to public/unlisted recipes and
just showing the title otherwise.

ShareMealPlanButton gained the same public-link toggle UI as its
shopping-list sibling, plus a QR code (generated client-side via the
already-installed `qrcode` package) for the link once enabled --
handing someone a printed or screenshotted plan doesn't require
typing a URL.

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

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 All notable changes to Epicure are documented here. This file is mirrored in-app at `/changelog` (and in the admin dashboard) via `apps/web/lib/changelog.ts` — update both together.
 
+## 0.68.0 — 2026-07-21 10:00
+
+### Added
+- Meal plans can now be shared with a read-only anonymous public link (Share → Public link), same idea as shopping lists' public link but view-only, plus a QR code you can screenshot or print to hand someone the week's plan.
+
 ## 0.67.0 — 2026-07-21 09:30
 
 ### Added