feat: implement MailModule with email services and tests

Added MailModule with services for email validation and password reset functionalities. Includes configuration via `@nestjs-modules/mailer` and comprehensive unit tests.

backend/src/mail/mail.module.ts

@@ -0,0 +1,29 @@
+import { Module } from "@nestjs/common";
+import { ConfigService } from "@nestjs/config";
+import { MailerModule } from "@nestjs-modules/mailer";
+import { MailService } from "./mail.service";
+
+@Module({
+	imports: [
+		MailerModule.forRootAsync({
+			useFactory: async (config: ConfigService) => ({
+				transport: {
+					host: config.get("MAIL_HOST"),
+					port: Number(config.get("MAIL_PORT")),
+					secure: config.get("MAIL_SECURE") === "true",
+					auth: {
+						user: config.get("MAIL_USER"),
+						pass: config.get("MAIL_PASS"),
+					},
+				},
+				defaults: {
+					from: `"No Reply" <${config.get("MAIL_FROM")}>`,
+				},
+			}),
+			inject: [ConfigService],
+		}),
+	],
+	providers: [MailService],
+	exports: [MailService],
+})
+export class MailModule {}