feat: one-click shopping list from meal plan, fix ingredient merge bug

- Meal-plan page now has a direct "Add to shopping list" action for the
  currently-viewed week, instead of requiring a trip to Shopping Lists and
  manually typing the week's Monday date.
- Fixed a real under-shopping bug in shopping-lists/route.ts: when
  generating from a meal-plan week, ingredients appearing in more than one
  recipe were merged by keeping only the FIRST occurrence's quantity and
  silently dropping the rest. New mergeIngredients() (pantry-shopping-match.ts)
  groups by ingredientId (or normalized name+unit) and sums quantities
  across every recipe in the week; incompatible/unparseable units are kept
  as separate line items rather than guessed at.

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

apps/web/app/api/v1/shopping-lists/route.ts

@@ -2,7 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import { z } from "zod";
 import { db, shoppingLists, shoppingListItems, mealPlans, mealPlanEntries, recipeIngredients, pantryItems, eq, and, desc, inArray } from "@epicure/db";
 import { requireSession } from "@/lib/api-auth";
-import { applyPantryToItems } from "@/lib/pantry-shopping-match";
+import { applyPantryToItems, mergeIngredients } from "@/lib/pantry-shopping-match";
 
 const CreateSchema = z.object({
   name: z.string().min(1).max(100),
@@ -54,20 +54,10 @@ export async function POST(req: NextRequest) {
           where: inArray(recipeIngredients.recipeId, recipeIds),
         });
 
-        // Simple merge by rawName (case-insensitive)
-        const merged = new Map<string, { rawName: string; quantity?: string; unit?: string; ingredientId: string | null }>();
-        for (const ing of ings) {
-          const key = ing.rawName.toLowerCase();
-          if (!merged.has(key)) {
-            merged.set(key, {
-              rawName: ing.rawName,
-              quantity: ing.quantity ?? undefined,
-              unit: ing.unit ?? undefined,
-              ingredientId: ing.ingredientId,
-            });
-          }
-        }
-        const mergedItems = Array.from(merged.values());
+        // Merge same ingredient across all of the week's recipes, summing quantities
+        // (grouped by ingredientId when available, else normalized name+unit) instead
+        // of listing it once per recipe or dropping every occurrence but the first.
+        const mergedItems = mergeIngredients(ings);
 
         // Reduce/flag quantities already covered by the user's pantry. Conservative: never silently
         // drops an item — fully-covered items are still inserted, flagged `inPantry`, so nothing