Rebrand: Co-op Check-in -> Co-op Survey in user-facing copy

Updates the tool product name across the app UI (header, page title,
section labels, form buttons, success/error states, report stat labels),
README, deployment docs, and the CiviCRM email template guidance.
Custom domain references move from check-in.fci.coop to survey.fci.coop
(DNS update still required).

The underlying CiviCRM "Check-in (organizing)" activity type, custom
group machine names (Check_in_data__organizing_), health-check ids,
and the internal org_engagement_check_in form id are unchanged --
those are CiviCRM contract surfaces, not product copy.

app/report/page.tsx

@@ -52,7 +52,7 @@ function ReportIntro() {
       </h1>
       <p className="mt-4 max-w-prose text-[17px] leading-relaxed text-ink-soft">
         A read-only summary of every value your co-op has shared through past
-        check-ins, grouped by stage. The most recent entry sits at the top of
+        surveys, grouped by stage. The most recent entry sits at the top of
         each row; expand a row to see how a number or note has changed over
         time.
       </p>