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"

app/pages/member/account.vue

@@ -283,7 +283,7 @@
                   form.contributionAmount === Number(memberData.contributionAmount || 0) ||
                   isUpdating
                 "
-                @click="handleUpdateTier"
+                @click="handleUpdateContribution"
               >
                 {{ isUpdating ? "Updating…" : "Update Contribution" }}
               </button>
@@ -482,7 +482,7 @@ const refreshNextBillingIfStale = async () => {
   }
 };
 
-const handleUpdateTier = async () => {
+const handleUpdateContribution = async () => {
   isUpdating.value = true;
   try {
     await $fetch("/api/members/update-contribution", {