Fix migration require paths after reorganization

- Updated all core migrations to use ../../src/ instead of ../src/
- Updated legacy migrations with the same path fix
- This fixes MODULE_NOT_FOUND errors during deployment

The error occurred because migrations were moved one level deeper
into core/ and legacy/ subdirectories without updating the relative
paths to the source files.

backend/migrations/core/init.js

@@ -1,6 +1,6 @@
 const bcrypt = require('bcrypt');
-const { db, initializeDatabase } = require('../src/database/db');
-const { generateReadablePassword } = require('../src/utils/passwordGenerator');
+const { db, initializeDatabase } = require('../../src/database/db');
+const { generateReadablePassword } = require('../../src/utils/passwordGenerator');
 const fs = require('fs').promises;
 const path = require('path');