chore(admin): rename pending_payment label and tier→contribution

Backlog cleanup from docs/LAUNCH_READINESS.md:
- B4: admin status filter + form options + STATUS_LABELS now read
  "Payment setup incomplete" so admins stop conflating with membership state
- CSV import preview header "Tier" → "Contribution"
- handleUpdateTier → handleUpdateContribution on /member/account
- update-contribution error log "tier" → "amount"

server/api/members/update-contribution.post.js

@@ -250,7 +250,7 @@ export default defineEventHandler(async (event) => {
     };
   } catch (error) {
     if (error.statusCode) throw error;
-    console.error("Error updating contribution tier:", error);
+    console.error("Error updating contribution amount:", error);
     throw createError({
       statusCode: 500,
       statusMessage: "An unexpected error occurred",