Refactor database configuration and enhance error handling in authentication services

Updated the database configuration to centralize settings and improve maintainability. Enhanced error handling in the authentication service to provide clearer and more specific error messages for various failure scenarios, including registration, activation, and login processes. Additionally, added new dependencies for testing and SQLite support in the package.json file.

backend/vitest.config.js

@@ -0,0 +1,14 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    globals: true,
+    environment: 'node',
+    setupFiles: ['./tests/setupTestEnv.js'],
+    include: ['tests/**/*.test.js'],
+    coverage: {
+      reporter: ['text', 'html'],
+      exclude: ['migrations/**', 'uploads/**', 'scripts/**'],
+    },
+  },
+});