Primer version funcional

database/migration_create_expense_concept_allocations_table.sql

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+-- Migration to create expense_concept_allocations table
+CREATE TABLE `expense_concept_allocations` (
+    `id` INT AUTO_INCREMENT PRIMARY KEY,
+    `expense_id` INT NOT NULL,
+    `concept_id` INT NOT NULL,
+    `amount` DECIMAL(10, 2) NOT NULL,
+    `created_at` DATETIME DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (`expense_id`) REFERENCES `expenses`(`id`) ON DELETE CASCADE,
+    FOREIGN KEY (`concept_id`) REFERENCES `finance_collection_concepts`(`id`) ON DELETE CASCADE,
+    UNIQUE KEY `unique_expense_concept_allocation` (`expense_id`, `concept_id`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;