feat(logistics): external attendees self-select lunch dish via tokenized page

External lunch attendees had no way to pick their own dish — an admin had to set
it inline and no email was ever sent. (Marine added herself as an external
expecting a dish-selection link and never received one.)

Adds:
- ExternalAttendee.inviteSentAt + additive migration
- HMAC-signed external lunch token (mirrors finalist-token)
- Public no-login picker page /lunch/pick/[token] — dish + allergens + notes,
  gated by the lunch change deadline, read-only after
- tRPC getExternalByToken / setExternalPick (public) + sendExternalInvite (admin)
- Auto-send invite on createExternal when an email is present; per-row resend
  button + status chip (Invited / Picked / no email) in the logistics screen
- Unpicked externals chased by the lunch reminder cron + manual "Send reminders"
- sendExternalDishInviteEmail (branded). Page + email title use the configurable
  venue ("Lunch at {venue}") rather than "grand finale"

Tests: token roundtrip/tamper/expiry, selectUnpickedExternals filter,
get/set-by-token happy + deadline + bad-token, createExternal auto-send,
cron external reminders. Full suite 303 passing; build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/server/services/lunch-external-invite.ts

@@ -0,0 +1,61 @@
+import type { Prisma, PrismaClient } from '@prisma/client'
+import { signExternalLunchToken } from '@/lib/external-lunch-token'
+import { getBaseUrl, sendExternalDishInviteEmail } from '@/lib/email'
+
+type PrismaLike = PrismaClient | Prisma.TransactionClient
+
+export type InvitableExternal = {
+  id: string
+  name: string
+  email: string | null
+}
+
+export type InviteLunchEvent = {
+  eventAt: Date | null
+  venue: string | null
+  notes: string | null
+  changeCutoffHours: number
+}
+
+/**
+ * Build the public, tokenized dish-pick URL for an external attendee.
+ * The token is a stateless HMAC signature (see external-lunch-token) carrying the
+ * externalId; `exp` is generous (event day + 1, or 30 days when no event date)
+ * so the link outlives the change deadline, which is enforced separately at write.
+ */
+export function buildExternalPickUrl(externalId: string, eventAt: Date | null): string {
+  const exp = eventAt
+    ? Math.floor(eventAt.getTime() / 1000) + 86_400
+    : Math.floor(Date.now() / 1000) + 30 * 86_400
+  const token = signExternalLunchToken({ externalId, exp })
+  return `${getBaseUrl()}/lunch/pick/${token}`
+}
+
+/**
+ * Send (or resend) the dish-selection invite to one external attendee and stamp
+ * `inviteSentAt`. Throws if the external has no email or the email send fails;
+ * callers that must not fail (e.g. createExternal) wrap this in try/catch.
+ */
+export async function sendExternalDishInvite(
+  prisma: PrismaLike,
+  external: InvitableExternal,
+  event: InviteLunchEvent,
+): Promise<void> {
+  if (!external.email) throw new Error('External attendee has no email address')
+  const changeDeadline = event.eventAt
+    ? new Date(event.eventAt.getTime() - event.changeCutoffHours * 3_600_000)
+    : null
+  await sendExternalDishInviteEmail({
+    to: external.email,
+    name: external.name,
+    eventAt: event.eventAt,
+    venue: event.venue,
+    notes: event.notes,
+    changeDeadline,
+    pickUrl: buildExternalPickUrl(external.id, event.eventAt),
+  })
+  await prisma.externalAttendee.update({
+    where: { id: external.id },
+    data: { inviteSentAt: new Date() },
+  })
+}

src/server/services/lunch-reminders.ts

@@ -30,3 +30,21 @@ export async function selectUnpickedAttendees(
     include: { user: { select: { name: true, email: true } } },
   })
 }
+
+/**
+ * Return external attendees for a LunchEvent that can still be chased for a dish
+ * pick: they have an email on file and have not yet been assigned a dish.
+ * Externals with no email (un-emailable) or an existing dish are excluded.
+ */
+export async function selectUnpickedExternals(
+  prisma: PrismaClient,
+  event: { id: string },
+) {
+  return prisma.externalAttendee.findMany({
+    where: {
+      lunchEventId: event.id,
+      dishId: null,
+      AND: [{ email: { not: null } }, { email: { not: '' } }],
+    },
+  })
+}