Distinguish picked-up from removed shopping list items

Soft-remove items via RemovedAt/RemovedByUserId instead of hard
deleting so the row survives for undo and future history reporting.
DELETE now sets the removal fields; a new POST .../restore clears
them. Active list reads (summary, detail, check toggle) filter to
RemovedAt IS NULL. Frontend surfaces an Undo toast on remove and
handles a new ItemRestored SignalR event.

src/backend/YesChef.Api/Migrations/YesChefDbModelSnapshot.cs

@@ -1,4 +1,4 @@
-// <auto-generated />
+// <auto-generated />
 using System;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Infrastructure;
@@ -223,6 +223,12 @@ namespace YesChef.Api.Migrations
                     b.Property<int?>("RecipeId")
                         .HasColumnType("integer");
 
+                    b.Property<DateTime?>("RemovedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int?>("RemovedByUserId")
+                        .HasColumnType("integer");
+
                     b.Property<int>("ShoppingListId")
                         .HasColumnType("integer");
 
@@ -237,6 +243,8 @@ namespace YesChef.Api.Migrations
 
                     b.HasIndex("RecipeId");
 
+                    b.HasIndex("RemovedByUserId");
+
                     b.HasIndex("ShoppingListId");
 
                     b.ToTable("ShoppingListItems");
@@ -402,6 +410,11 @@ namespace YesChef.Api.Migrations
                         .HasForeignKey("RecipeId")
                         .OnDelete(DeleteBehavior.SetNull);
 
+                    b.HasOne("YesChef.Api.Entities.User", "RemovedByUser")
+                        .WithMany()
+                        .HasForeignKey("RemovedByUserId")
+                        .OnDelete(DeleteBehavior.SetNull);
+
                     b.HasOne("YesChef.Api.Entities.ShoppingList", "ShoppingList")
                         .WithMany("Items")
                         .HasForeignKey("ShoppingListId")
@@ -414,6 +427,8 @@ namespace YesChef.Api.Migrations
 
                     b.Navigation("Recipe");
 
+                    b.Navigation("RemovedByUser");
+
                     b.Navigation("ShoppingList");
                 });