Add email-based invites and email confirmation in one flow

Family admins can now invite new members by email. The recipient gets a
templated email with a single-use, time-limited join link; clicking it
opens the registration form bound to the invite, and submitting the
form simultaneously consumes the invite and marks the email confirmed.
Self-registration via the shareable family code remains available.

Backend
- New Invite entity (token hash only — raw token never stored), with
  per-family uniqueness on the active hash.
- User gains nullable Email and EmailConfirmedAt; partial unique index
  so legacy rows with no email do not collide.
- /api/family/invites — admin endpoints to list pending, issue, resend
  (rotates the token), and revoke.
- /api/auth/invite/{token} — public lookup returning email + family name
  so the registration form can show "you have been invited to X".
- /api/auth/register accepts InviteToken; the invite vouches for the
  email, so any client-supplied email field is ignored. Falls back to
  FamilyCode when no invite token is present.
- AppUrlOptions / AppBaseUrl plumbed through so emails build absolute
  links to the deployed frontend.

Frontend
- /login reads ?invite=<token>, looks it up, and switches the form into
  invite-registration mode (pre-binding to the invited email + family).
- /family admin section gains an invite-by-email form, a pending list,
  and resend/revoke actions with a confirmation modal.

Tests
- 14 new integration tests covering: admin issue, member-forbidden,
  lookup, valid/expired/consumed/unknown-token registration, resend
  rotation, revocation, pending-only list filter, and conflict for
  inviting an existing member. RecordingEmailSender captures dispatched
  messages so tests can assert on the link without standing up SMTP.

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

@@ -72,6 +72,56 @@ namespace YesChef.Api.Migrations
                     b.ToTable("FamilyMemberships");
                 });
 
+            modelBuilder.Entity("YesChef.Api.Entities.Invite", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("integer");
+
+                    NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b.Property<int>("Id"));
+
+                    b.Property<DateTime?>("ConsumedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int?>("ConsumedByUserId")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("Email")
+                        .IsRequired()
+                        .HasMaxLength(254)
+                        .HasColumnType("character varying(254)");
+
+                    b.Property<DateTime>("ExpiresAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int>("FamilyId")
+                        .HasColumnType("integer");
+
+                    b.Property<DateTime>("IssuedAt")
+                        .HasColumnType("timestamp with time zone");
+
+                    b.Property<int>("IssuedByUserId")
+                        .HasColumnType("integer");
+
+                    b.Property<string>("TokenHash")
+                        .IsRequired()
+                        .HasMaxLength(64)
+                        .HasColumnType("character varying(64)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("ConsumedByUserId");
+
+                    b.HasIndex("IssuedByUserId");
+
+                    b.HasIndex("TokenHash")
+                        .IsUnique();
+
+                    b.HasIndex("FamilyId", "ConsumedAt");
+
+                    b.ToTable("Invites");
+                });
+
             modelBuilder.Entity("YesChef.Api.Entities.Recipe", b =>
                 {
                     b.Property<int>("Id")
@@ -328,6 +378,13 @@ namespace YesChef.Api.Migrations
                     b.Property<DateTime>("CreatedAt")
                         .HasColumnType("timestamp with time zone");
 
+                    b.Property<string>("Email")
+                        .HasMaxLength(254)
+                        .HasColumnType("character varying(254)");
+
+                    b.Property<DateTime?>("EmailConfirmedAt")
+                        .HasColumnType("timestamp with time zone");
+
                     b.Property<string>("Name")
                         .IsRequired()
                         .HasMaxLength(100)
@@ -339,6 +396,10 @@ namespace YesChef.Api.Migrations
 
                     b.HasKey("Id");
 
+                    b.HasIndex("Email")
+                        .IsUnique()
+                        .HasFilter("\"Email\" IS NOT NULL");
+
                     b.HasIndex("Name")
                         .IsUnique();
 
@@ -364,6 +425,32 @@ namespace YesChef.Api.Migrations
                     b.Navigation("User");
                 });
 
+            modelBuilder.Entity("YesChef.Api.Entities.Invite", b =>
+                {
+                    b.HasOne("YesChef.Api.Entities.User", "ConsumedByUser")
+                        .WithMany()
+                        .HasForeignKey("ConsumedByUserId")
+                        .OnDelete(DeleteBehavior.SetNull);
+
+                    b.HasOne("YesChef.Api.Entities.Family", "Family")
+                        .WithMany()
+                        .HasForeignKey("FamilyId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.HasOne("YesChef.Api.Entities.User", "IssuedByUser")
+                        .WithMany()
+                        .HasForeignKey("IssuedByUserId")
+                        .OnDelete(DeleteBehavior.Restrict)
+                        .IsRequired();
+
+                    b.Navigation("ConsumedByUser");
+
+                    b.Navigation("Family");
+
+                    b.Navigation("IssuedByUser");
+                });
+
             modelBuilder.Entity("YesChef.Api.Entities.Recipe", b =>
                 {
                     b.HasOne("YesChef.Api.Entities.User", "CreatedByUser")