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>

pnpm-lock.yaml

@@ -56,6 +56,9 @@ importers:
       cmdk:
         specifier: ^1.1.1
         version: 1.1.1(@types/react-dom@19.2.3(@types/react@19.2.17))(@types/react@19.2.17)(react-dom@19.2.4(react@19.2.4))(react@19.2.4)
+      diff:
+        specifier: ^9.0.0
+        version: 9.0.0
       drizzle-orm:
         specifier: ^0.44.7
         version: 0.44.7(@opentelemetry/api@1.9.1)(kysely@0.29.2)(postgres@3.4.9)
@@ -176,6 +179,9 @@ importers:
         specifier: ^3.4.7
         version: 3.4.9
     devDependencies:
+      '@types/node':
+        specifier: ^20.19.43
+        version: 20.19.43
       drizzle-kit:
         specifier: ^0.31.1
         version: 0.31.10
@@ -2982,6 +2988,10 @@ packages:
     resolution: {integrity: sha512-DPi0FmjiSU5EvQV0++GFDOJ9ASQUVFh5kD+OzOnYdi7n3Wpm9hWWGfB/O2blfHcMVTL5WkQXSnRiK9makhrcnw==}
     engines: {node: '>=0.3.1'}
 
+  diff@9.0.0:
+    resolution: {integrity: sha512-svtcdpS8CgJyqAjEQIXdb3OjhFVVYjzGAPO8WGCmRbrml64SPw/jJD4GoE98aR7r25A0XcgrK3F02yw9R/vhQw==}
+    engines: {node: '>=0.3.1'}
+
   doctrine@2.1.0:
     resolution: {integrity: sha512-35mSku4ZXK0vfCuHEDAwt55dg2jNajHZ1odvF+8SSr82EsZY4QmXfuWso8oEd8zRhVObSN18aM0CjSdoBX7zIw==}
     engines: {node: '>=0.10.0'}
@@ -7865,6 +7875,8 @@ snapshots:
 
   diff@8.0.4: {}
 
+  diff@9.0.0: {}
+
   doctrine@2.1.0:
     dependencies:
       esutils: 2.0.3