Add member_contact table and postal_code column to member table

Created a new SQL migration to add a postal_code column to the member table and introduced a member_contact table to store multiple phone numbers and email addresses. Implemented data migration for existing phone numbers and email addresses from the member table to the new member_contact table, ensuring data integrity and improved contact management.

backend/migrations/add_member_contact_and_postal_code.sql

@@ -0,0 +1,57 @@
+-- Add postal_code column to member table
+ALTER TABLE `member` 
+ADD COLUMN `postal_code` TEXT NULL COMMENT 'Postal code (PLZ)' AFTER `city`;
+
+-- Create member_contact table for multiple phone numbers and email addresses
+CREATE TABLE IF NOT EXISTS `member_contact` (
+  `id` INT NOT NULL AUTO_INCREMENT,
+  `member_id` INT NOT NULL,
+  `type` ENUM('phone', 'email') NOT NULL COMMENT 'Type of contact: phone or email',
+  `value` TEXT NOT NULL,
+  `is_parent` BOOLEAN NOT NULL DEFAULT FALSE COMMENT 'Whether this contact belongs to a parent',
+  `parent_name` TEXT NULL COMMENT 'Name of the parent (e.g. "Mutter", "Vater", "Elternteil 1")',
+  `is_primary` BOOLEAN NOT NULL DEFAULT FALSE COMMENT 'Whether this is the primary contact of this type',
+  `created_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  `updated_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  PRIMARY KEY (`id`),
+  INDEX `idx_member_id` (`member_id`),
+  INDEX `idx_type` (`type`),
+  CONSTRAINT `fk_member_contact_member` 
+    FOREIGN KEY (`member_id`) 
+    REFERENCES `member` (`id`) 
+    ON DELETE CASCADE 
+    ON UPDATE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+-- Migrate existing phone numbers from member.phone to member_contact
+INSERT INTO `member_contact` (`member_id`, `type`, `value`, `is_parent`, `parent_name`, `is_primary`, `created_at`, `updated_at`)
+SELECT 
+    `id` AS `member_id`,
+    'phone' AS `type`,
+    `phone` AS `value`,
+    FALSE AS `is_parent`,
+    NULL AS `parent_name`,
+    TRUE AS `is_primary`,
+    NOW() AS `created_at`,
+    NOW() AS `updated_at`
+FROM `member`
+WHERE `phone` IS NOT NULL 
+  AND `phone` != ''
+  AND TRIM(`phone`) != '';
+
+-- Migrate existing email addresses from member.email to member_contact
+INSERT INTO `member_contact` (`member_id`, `type`, `value`, `is_parent`, `parent_name`, `is_primary`, `created_at`, `updated_at`)
+SELECT 
+    `id` AS `member_id`,
+    'email' AS `type`,
+    `email` AS `value`,
+    FALSE AS `is_parent`,
+    NULL AS `parent_name`,
+    TRUE AS `is_primary`,
+    NOW() AS `created_at`,
+    NOW() AS `updated_at`
+FROM `member`
+WHERE `email` IS NOT NULL 
+  AND `email` != ''
+  AND TRIM(`email`) != '';
+