Add standalone tire review page for social sharing

Create a shareable standalone page at /tire-review/ where visitors can
select a tire and submit a review without navigating the full catalog.
Supports deep-linking via ?tire=TIRE_ID with tire-specific OG/Twitter
meta tags for rich social previews.

- New RTG_Tire_Review controller (rewrite rule + template_redirect)
- Standalone HTML template with dark theme, inline review form
- Searchable tire dropdown with live filtering
- Reuses existing AJAX review submission handlers
- Configurable slug in Settings (default: tire-review)

https://claude.ai/code/session_01BAc9aiNw9dh4GeqEkpkxLK

Author: claude

admin/views/settings.php

@@ -10,6 +10,7 @@
 $cdn_prefix = $settings['cdn_prefix'] ?? '';
 $compare_slug = $settings['compare_slug'] ?? 'tire-compare';
 $user_reviews_slug = $settings['user_reviews_slug'] ?? 'user-reviews';
+$tire_review_slug = $settings['tire_review_slug'] ?? 'tire-review';
 
 // Theme color defaults.
 $default_colors = array(
@@ -102,6 +103,13 @@
                     <p class="rtg-field-description">Page slug where the <code>[rivian_user_reviews]</code> shortcode is placed. Default: <code>user-reviews</code> (accessible at <code><?php echo esc_html( home_url( '/' . $user_reviews_slug . '/' ) ); ?></code>)</p>
                     <input type="text" id="user_reviews_slug" name="user_reviews_slug" value="<?php echo esc_attr( $user_reviews_slug ); ?>">
                 </div>
+                <div class="rtg-field-row">
+                    <div class="rtg-field-label-row">
+                        <label class="rtg-field-label" for="tire_review_slug">Tire Review Page Slug</label>
+                    </div>
+                    <p class="rtg-field-description">URL slug for the standalone tire review page. Default: <code>tire-review</code> (accessible at <code><?php echo esc_html( home_url( '/' . $tire_review_slug . '/' ) ); ?></code>)</p>
+                    <input type="text" id="tire_review_slug" name="tire_review_slug" value="<?php echo esc_attr( $tire_review_slug ); ?>">
+                </div>
             </div>
         </div>