Implement Phase 7: Contact Form 7 Integration (v0.7.0)

Add custom CF7 form tags for booking requests:
- [bnb_building_select] - Building filter dropdown
- [bnb_room_select] - Room selection with capacity data
- [bnb_date_checkin/checkout] - Date pickers with validation
- [bnb_guests] - Guest count with capacity limits

Features:
- Server-side validation for all fields
- Real-time AJAX availability checking
- Automatic price calculation display
- Booking creation on form submission
- Guest record creation/linking
- Custom mail tags for CF7 templates

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

wp-bnb.php

@@ -3,7 +3,7 @@
  * Plugin Name: WP BnB Management
  * Plugin URI: https://src.bundespruefstelle.ch/magdev/wp-bnb
  * Description: A comprehensive Bed & Breakfast management system for WordPress. Manage buildings, rooms, bookings, and guests.
- * Version: 0.6.1
+ * Version: 0.7.0
  * Requires at least: 6.0
  * Requires PHP: 8.3
  * Author: Marco Graetsch
@@ -24,7 +24,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 }
 
 // Plugin version constant - MUST match Version in header above.
-define( 'WP_BNB_VERSION', '0.6.1' );
+define( 'WP_BNB_VERSION', '0.7.0' );
 
 // Plugin path constants.
 define( 'WP_BNB_PATH', plugin_dir_path( __FILE__ ) );