feat: 6 new per-tier feature flags (off by default) + flag-icon locale switcher + hide BYOK when disabled (v0.74.0)

Extends the existing feature-flags system (previously 3 keys, all
default-enabled) with 6 more: recipe_import_url, recipe_import_photo,
nutrition_estimation, markdown_export, weekly_nutrition,
grocery_delivery. Each FEATURE_DEFINITIONS entry now carries its own
defaultEnabled -- the new 6 default to false, the original 3 stay
true -- so no migration/seed was needed for the "off by default"
requirement, just a per-key fallback instead of a blanket true.

Gated server-side (requireFeatureEnabledResponse, a new shared
helper avoiding six copies of the same try/catch) on: import-url,
import-photo, nutrition POST estimate, bulk markdown export, weekly
meal-plan nutrition GET, Instacart export. Gated client-side by
hiding the trigger entirely (not just disabling) on every page that
renders one: recipe detail (meal/drink pairing buttons, nutrition
panel's estimate button, markdown export), recipes list (import-URL
button, including the OS Share Target auto-import path), new-recipe
page (photo import), meal-plan page (markdown export, weekly
nutrition bar), shopping-list/collection/pantry pages (markdown
export), shopping-list page (Instacart button, now gated by both the
existing env-var check AND the tier flag).

Also: BYOK section on Settings -> AI now hidden entirely for
non-BYOK users (previously showed a locked-and-teased notice, same
inconsistency the Model Prefs fix closed yesterday). Language
switcher shows a flag icon (FlagGB/FlagFR, moved from
components/marketing to components/shared so both the logged-in
settings switcher and the logged-out marketing one can use it)
instead of plain "English"/"Français" text-only options.

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

apps/web/app/(app)/pantry/page.tsx

@@ -10,12 +10,15 @@ import { ExpiringLeftovers } from "@/components/pantry/expiring-leftovers";
 import { scoreRecipesAgainstPantry } from "@/lib/pantry-match";
 import { dishExpiresAt, daysUntil, isLeftoverExpiringSoon } from "@/lib/leftover-match";
 import { getPublicUrl } from "@/lib/storage";
+import { getFeatureFlagMatrix, type Tier } from "@/lib/feature-flags";
 
 export const metadata: Metadata = {};
 
 export default async function PantryPage() {
   const session = await auth.api.getSession({ headers: await headers() });
   if (!session) return null;
+  const viewerTier = (session.user as { tier?: string }).tier as Tier | undefined ?? "free";
+  const canExportMarkdown = (await getFeatureFlagMatrix()).markdown_export[viewerTier];
 
   const [items, candidateRecipes, cookedDishes] = await Promise.all([
     db.query.pantryItems.findMany({
@@ -75,7 +78,7 @@ export default async function PantryPage() {
 
   return (
     <div className="space-y-6">
-      <PantryPageHeader items={mappedItems} />
+      <PantryPageHeader items={mappedItems} canExportMarkdown={canExportMarkdown} />
       <ExpiringLeftovers leftovers={leftovers} />
       <ExpiringSoonSuggestions suggestions={suggestions} />
       <PantryManager key={mappedItems.map((i) => i.id).join(",")} initialItems={mappedItems} />