Release version 1.1.19 - Enhanced duplicate detection

Fixed persistent duplicate settings page by improving duplicate detection
to check by class type and ID instead of strict instance comparison.

Issue:
- Strict instance comparison (===) failed to detect duplicates
- Different object instances of same class not caught by previous check
- Settings page still appearing twice despite singleton and instance caching

Solution:
- Changed duplicate detection from instance comparison to type/ID checks
- Added instanceof WC_TPP_Settings check
- Added get_id() method check for ID 'tier_package_prices'
- Added direct id property check as fallback
- Multiple layers of detection to catch duplicates regardless of how created

Fixes:
- Settings page rendering twice in WooCommerce backend
- Duplicate detection failing for different instances of same class

Changes:
- Enhanced add_settings_page() with multi-layer duplicate detection
- Checks: instanceof, get_id(), and id property
- Returns early if any existing page matches criteria

Technical Details:
- Strict comparison only works if exact same object instance
- Different instances (even of same class/ID) fail === check
- instanceof checks class type regardless of which instance
- ID checks ensure no duplicate pages with same identifier
- Fallback checks handle different WooCommerce versions/implementations

Updated Files:
- includes/class-wc-tpp-admin.php (enhanced duplicate detection)
- wc-tier-and-package-prices.php (version 1.1.19)
- composer.json (version 1.1.19)
- CHANGELOG.md (v1.1.19 section)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

includes/class-wc-tpp-admin.php

@@ -35,8 +35,21 @@ if (!class_exists('WC_TPP_Admin')) {
         }
 
         // Check if our settings page is already in the array to prevent duplicates
+        // Check by class type and ID instead of instance comparison
         foreach ($settings as $settings_page) {
-            if ($settings_page === self::$settings_instance) {
+            if ($settings_page instanceof WC_TPP_Settings) {
+                return $settings;
+            }
+            // Also check by ID property if it's a WC_Settings_Page
+            if (is_object($settings_page) &&
+                method_exists($settings_page, 'get_id') &&
+                $settings_page->get_id() === 'tier_package_prices') {
+                return $settings;
+            }
+            // Check id property directly
+            if (is_object($settings_page) &&
+                isset($settings_page->id) &&
+                $settings_page->id === 'tier_package_prices') {
                 return $settings;
             }
         }