fix(instanda): rate limiting, UTC timestamps, and close silent-failure paths

- F-06: throttle the public create per IP (20/h) and per email (5/h) before the
  paid API call and the PII write.
- F-11: wrap the create path in try/catch - on an unexpected error fail closed for
  that submission (no quote-less entry), alert admins, keep the form working.
- F-14: abort the StartQuote when the write-ahead insert fails (no unaudited call);
  fire the failure alert even when storage is disabled (build an in-memory tx).
- F-10/F-17: treat a 2xx with a missing/empty quoteRef as ambiguous
  (possible_duplicate=1), not a hard failure - a quote may exist.
- F-07: write created_at/delivered_at/event timestamps in UTC to match the gmdate()
  retention/dedupe cutoffs; display in site-local via get_date_from_gmt.
- F-09: log (no silent return) when async record_feed_result cannot resolve a
  delivered transaction.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

wp-content/plugins/esp-instanda-integration/includes/class-transaction-store.php

@@ -137,7 +137,7 @@ final class Transaction_Store {
     /** Write-ahead insert. Returns the new row id (0 on failure). */
     public function create_pending(Transaction $t): int {
         global $wpdb;
-        $now = current_time('mysql');
+        $now = current_time('mysql', true); // UTC - matches the gmdate() retention/dedupe cutoffs
         $t->event_log[] = self::event('Write-ahead record created (status: pending)');
 
         $ok = $wpdb->insert(self::table_name(), [
@@ -159,14 +159,14 @@ final class Transaction_Store {
     }
 
     public function mark_success(int $id, string $quote_ref, ?string $quote_url, ?int $http_status): void {
-        $delivered = current_time('mysql');
+        $delivered = current_time('mysql', true); // UTC
         $this->update($id, [
             'status'           => Tx_Status::Delivered->value,
             'quote_ref'        => $quote_ref,
             'quote_url'        => $quote_url,
             'http_status'      => $http_status,
             'delivered_at'     => $delivered,
-            'expiry'           => $this->compute_expiry($delivered),
+            'expiry'           => $this->compute_expiry(),
         ], 'Delivered - quoteRef ' . $quote_ref);
     }
 
@@ -375,14 +375,14 @@ final class Transaction_Store {
         $wpdb->update(self::table_name(), $data, ['id' => $id]);
     }
 
-    private function compute_expiry(string $delivered_at): string {
+    /** Expiry = now + retention window, in UTC (delivered_at is written at ~the same instant). */
+    private function compute_expiry(): string {
         $days = (int) get_option('espinstanda_retention_days', 7);
-        $ts   = strtotime($delivered_at) ?: time();
-        return gmdate('Y-m-d H:i:s', $ts + ($days * DAY_IN_SECONDS));
+        return gmdate('Y-m-d H:i:s', time() + ($days * DAY_IN_SECONDS));
     }
 
     /** @return array{ts:string,level:string,message:string} */
     private static function event(string $message, string $level = 'info'): array {
-        return ['ts' => current_time('mysql'), 'level' => $level, 'message' => Logger::redact($message)];
+        return ['ts' => current_time('mysql', true), 'level' => $level, 'message' => Logger::redact($message)];
     }
 }