feat: implement remaining TODO.md feature ideas + fix mobile headers

Implements the six previously-unscoped feature ideas plus a mobile
layout fix reported via screenshot:

- Mobile: Recipes/Collections/Pantry/Meal Plan/Shopping Lists headers
  now stack and wrap instead of clipping buttons on narrow viewports.
- Recipe diff/compare view: word/list diff against any past version,
  next to Restore in version history.
- Shared meal plans & shopping lists: new shoppingListMembers/
  mealPlanMembers tables (viewer/editor roles, mirrors
  collectionMembers), share dialogs, membership-checked routes.
- PDF cookbook export: /print/collection/[id] renders a whole
  collection with page breaks, using the existing print-CSS pattern
  instead of adding a PDF rendering dependency.
- Grocery delivery handoff: shopping lists can copy-as-text (works
  today) or send to Instacart once INSTACART_API_KEY is configured
  (stub adapter — real API needs a partner agreement).
- Personalized "For You" feed tab: ranks public recipes by tag/
  dietary overlap with the user's favorited/highly-rated history.
- PWA: added manifest.json + icons on top of the existing service
  worker so the app is installable; cook-mode pages were already
  cached for offline use.

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

apps/web/app/(app)/shopping-lists/[id]/page.tsx

@@ -4,10 +4,13 @@ import { headers } from "next/headers";
 import Link from "next/link";
 import { Printer } from "lucide-react";
 import { auth } from "@/lib/auth/server";
-import { db, shoppingLists, eq, and } from "@epicure/db";
+import { db, shoppingLists, eq } from "@epicure/db";
 import { ShoppingListView } from "@/components/meal-plan/shopping-list-view";
+import { ShareShoppingListButton } from "@/components/shopping-lists/share-shopping-list-button";
+import { GroceryExportButton } from "@/components/shopping-lists/grocery-export-button";
 import { buttonVariants } from "@/components/ui/button";
 import { cn } from "@/lib/utils";
+import { getShoppingListAccess, canWriteShoppingList } from "@/lib/shopping-list-access";
 
 type Params = { params: Promise<{ id: string }> };
 
@@ -18,29 +21,39 @@ export default async function ShoppingListPage({ params }: Params) {
   const session = await auth.api.getSession({ headers: await headers() });
   if (!session) return null;
 
+  const access = await getShoppingListAccess(id, session.user.id);
+  if (!access) notFound();
+
   const list = await db.query.shoppingLists.findFirst({
-    where: and(eq(shoppingLists.id, id), eq(shoppingLists.userId, session.user.id)),
+    where: eq(shoppingLists.id, id),
     with: { items: { orderBy: (t, { asc }) => [asc(t.aisle), asc(t.rawName)] } },
   });
-
   if (!list) notFound();
 
+  const canEdit = canWriteShoppingList(access.role);
+  const instacartEnabled = process.env["NEXT_PUBLIC_GROCERY_PROVIDER"] === "instacart";
+
   return (
     <div className="space-y-6 max-w-lg">
-      <div className="flex items-start justify-between">
+      <div className="flex flex-col gap-3 sm:flex-row sm:items-start sm:justify-between">
         <div>
           <h1 className="text-3xl font-bold tracking-tight">{list.name}</h1>
           <p className="text-muted-foreground mt-1">
             {list.items.length} items{list.generatedAt ? " · Generated from meal plan" : ""}
           </p>
         </div>
-        <Link href={`/print/shopping-list/${id}`} target="_blank" className={cn(buttonVariants({ variant: "outline", size: "sm" }))}>
-          <Printer className="h-4 w-4" />
-          Print
-        </Link>
+        <div className="flex flex-wrap items-center gap-2">
+          <GroceryExportButton listId={id} instacartEnabled={instacartEnabled} />
+          {access.role === "owner" && <ShareShoppingListButton listId={id} />}
+          <Link href={`/print/shopping-list/${id}`} target="_blank" className={cn(buttonVariants({ variant: "outline", size: "sm" }))}>
+            <Printer className="h-4 w-4" />
+            Print
+          </Link>
+        </div>
       </div>
       <ShoppingListView
         listId={id}
+        readOnly={!canEdit}
         initialItems={list.items.map((i) => ({
           id: i.id,
           rawName: i.rawName,

apps/web/app/(app)/shopping-lists/page.tsx

@@ -1,7 +1,7 @@
 import type { Metadata } from "next";
 import { headers } from "next/headers";
 import { auth } from "@/lib/auth/server";
-import { db, shoppingLists, eq, desc } from "@epicure/db";
+import { db, shoppingLists, shoppingListMembers, eq, desc } from "@epicure/db";
 import { ShoppingListsPageContent } from "@/components/shopping-lists/shopping-lists-page-content";
 
 export const metadata: Metadata = { title: "Shopping Lists" };
@@ -10,11 +10,17 @@ export default async function ShoppingListsPage() {
   const session = await auth.api.getSession({ headers: await headers() });
   if (!session) return null;
 
-  const lists = await db.query.shoppingLists.findMany({
-    where: eq(shoppingLists.userId, session.user.id),
-    orderBy: desc(shoppingLists.createdAt),
-    with: { items: { columns: { id: true, checked: true } } },
-  });
+  const [lists, memberships] = await Promise.all([
+    db.query.shoppingLists.findMany({
+      where: eq(shoppingLists.userId, session.user.id),
+      orderBy: desc(shoppingLists.createdAt),
+      with: { items: { columns: { id: true, checked: true } } },
+    }),
+    db.query.shoppingListMembers.findMany({
+      where: eq(shoppingListMembers.userId, session.user.id),
+      with: { list: { with: { user: true } } },
+    }),
+  ]);
 
   return (
     <ShoppingListsPageContent
@@ -25,6 +31,12 @@ export default async function ShoppingListsPage() {
         totalItems: list.items.length,
         checkedItems: list.items.filter((i) => i.checked).length,
       }))}
+      sharedLists={memberships.map((m) => ({
+        id: m.list.id,
+        name: m.list.name,
+        ownerName: m.list.user?.name ?? "Unknown",
+        role: m.role,
+      }))}
     />
   );
 }