Release version 1.1.5 - Critical bug fix for plugin activation

CRITICAL FIX: Resolved fatal error that prevented plugin activation in
versions 1.1.3 and 1.1.4. The add_cart_quantity_css() method was attempting
to access WooCommerce cart object during wp_head action, causing failures
when WooCommerce wasn't fully initialized or on admin pages.

Fixes:
- Plugin activation error in v1.1.3 and v1.1.4
- Fatal error when WooCommerce cart object not available
- Frontend errors on admin pages
- Issues during plugin initialization

Technical Changes:
- Added function_exists('WC') check before accessing WooCommerce
- Added is_admin() check to prevent CSS injection on admin pages
- Enhanced add_cart_quantity_css() with proper guards
- Line 191: if (!function_exists('WC') || !WC()->cart || is_admin())

Root Cause:
The add_cart_quantity_css() method (added in v1.1.3) hooks into wp_head
but didn't properly check if WooCommerce cart was available, causing
errors during plugin activation and on admin pages.

Updated Files:
- includes/class-wc-tpp-cart.php (enhanced error checking)
- wc-tier-and-package-prices.php (version 1.1.5)
- composer.json (version 1.1.5)
- CHANGELOG.md (v1.1.5 section)
- All translation files (.pot, .po, .mo) updated to version 1.1.5

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

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

languages/wc-tier-package-prices-de_CH_informal.po

@@ -3,7 +3,7 @@
 # This file is distributed under the GPL v2 or later.
 msgid ""
 msgstr ""
-"Project-Id-Version: WooCommerce Tier and Package Prices 1.1.4\n"
+"Project-Id-Version: WooCommerce Tier and Package Prices 1.1.5\n"
 "Report-Msgid-Bugs-To: https://src.bundespruefstelle.ch/wc-tier-package-prices\n"
 "POT-Creation-Date: 2025-12-21 00:00+0000\n"
 "PO-Revision-Date: 2025-12-21 00:00+0000\n"