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/lib/__tests__/for-you-ranking.test.ts

@@ -0,0 +1,56 @@
+import { describe, it, expect } from "vitest";
+import { buildPreferenceMap, scoreCandidate, rankForYou } from "../for-you-ranking";
+
+describe("buildPreferenceMap", () => {
+  it("counts tags and true dietary-tag keys across liked recipes", () => {
+    const map = buildPreferenceMap([
+      { tags: ["spicy", "quick"], dietaryTags: { vegan: true, glutenFree: false } },
+      { tags: ["spicy"], dietaryTags: null },
+    ]);
+    expect(map.get("spicy")).toBe(2);
+    expect(map.get("quick")).toBe(1);
+    expect(map.get("vegan")).toBe(1);
+    expect(map.get("glutenFree")).toBeUndefined();
+  });
+
+  it("returns an empty map for no liked recipes", () => {
+    expect(buildPreferenceMap([]).size).toBe(0);
+  });
+});
+
+describe("scoreCandidate", () => {
+  it("sums preference weights for overlapping tags", () => {
+    const prefs = new Map([["spicy", 3], ["vegan", 1]]);
+    const score = scoreCandidate({ tags: ["spicy"], dietaryTags: { vegan: true } }, prefs);
+    expect(score).toBe(4);
+  });
+
+  it("scores 0 when nothing overlaps", () => {
+    const prefs = new Map([["spicy", 3]]);
+    expect(scoreCandidate({ tags: ["sweet"], dietaryTags: null }, prefs)).toBe(0);
+  });
+});
+
+describe("rankForYou", () => {
+  const base = { dietaryTags: null };
+
+  it("sorts by score descending", () => {
+    const prefs = new Map([["spicy", 5]]);
+    const candidates = [
+      { id: "a", tags: ["sweet"], createdAt: new Date("2024-01-01"), ...base },
+      { id: "b", tags: ["spicy"], createdAt: new Date("2024-01-01"), ...base },
+    ];
+    const ranked = rankForYou(candidates, prefs);
+    expect(ranked.map((r) => r.id)).toEqual(["b", "a"]);
+  });
+
+  it("breaks ties by recency", () => {
+    const prefs = new Map<string, number>();
+    const candidates = [
+      { id: "old", tags: [], createdAt: new Date("2024-01-01"), ...base },
+      { id: "new", tags: [], createdAt: new Date("2024-06-01"), ...base },
+    ];
+    const ranked = rankForYou(candidates, prefs);
+    expect(ranked.map((r) => r.id)).toEqual(["new", "old"]);
+  });
+});