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/api/submit/route.ts

@@ -70,7 +70,7 @@ export async function POST(req: Request) {
     return NextResponse.json(
       {
         error: appEnv().isProduction
-          ? "Could not save your check-in. Please try again, or contact your engagement coordinator."
+          ? "Could not save your survey. Please try again, or contact your engagement coordinator."
           : `Save failed: ${redact(msg)}`,
       },
       { status: 500 },
@@ -110,7 +110,7 @@ async function runSubmit(cid: string, cs: string, values: Record<string, unknown
     "status_id:name": "Completed",
     target_contact_id: orgId,
     source_contact_id: Number(cid),
-    subject: "Co-op Check-in (form submission)",
+    subject: "Co-op Survey (form submission)",
   };
   for (const [name, value] of Object.entries(values)) {
     const field = FIELD_BY_NAME.get(name);