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.service.ts

@@ -0,0 +1,62 @@
+import { Injectable, Logger } from "@nestjs/common";
+import { ConfigService } from "@nestjs/config";
+import { MailerService } from "@nestjs-modules/mailer";
+
+@Injectable()
+export class MailService {
+	private readonly logger = new Logger(MailService.name);
+	private readonly domain: string;
+
+	constructor(
+		private mailerService: MailerService,
+		private configService: ConfigService,
+	) {
+		this.domain = this.configService.get<string>("DOMAIN_NAME", "memegoat.io");
+	}
+
+	async sendEmailValidation(email: string, token: string) {
+		const url = `https://${this.domain}/api/auth/verify-email?token=${token}`;
+
+		try {
+			await this.mailerService.sendMail({
+				to: email,
+				subject: "Validation de votre adresse email",
+				html: `
+        <p>Bonjour,</p>
+        <p>Veuillez cliquer sur le lien ci-dessous pour valider votre adresse email :</p>
+        <p><a href="${url}">${url}</a></p>
+        <p>Si vous n'avez pas demandé cette validation, vous pouvez ignorer cet email.</p>
+      `,
+			});
+		} catch (error) {
+			this.logger.error(
+				`Failed to send validation email to ${email}: ${error.message}`,
+				error.stack,
+			);
+			throw error;
+		}
+	}
+
+	async sendPasswordReset(email: string, token: string) {
+		const url = `https://${this.domain}/api/auth/reset-password?token=${token}`;
+
+		try {
+			await this.mailerService.sendMail({
+				to: email,
+				subject: "Réinitialisation de votre mot de passe",
+				html: `
+        <p>Bonjour,</p>
+        <p>Veuillez cliquer sur le lien ci-dessous pour réinitialiser votre mot de passe :</p>
+        <p><a href="${url}">${url}</a></p>
+        <p>Si vous n'avez pas demandé de réinitialisation, vous pouvez ignorer cet email.</p>
+      `,
+			});
+		} catch (error) {
+			this.logger.error(
+				`Failed to send password reset email to ${email}: ${error.message}`,
+				error.stack,
+			);
+			throw error;
+		}
+	}
+}