feat: add CommonModule with PurgeService and global exception filter

Introduced CommonModule to centralize shared functionality. Added PurgeService for automated database cleanup and a global exception filter for unified error handling.

backend/src/common/services/purge.service.ts

@@ -0,0 +1,63 @@
+import { Injectable, Logger } from "@nestjs/common";
+import { Cron, CronExpression } from "@nestjs/schedule";
+import { and, eq, isNotNull, lte } from "drizzle-orm";
+import { DatabaseService } from "../../database/database.service";
+import { contents, reports, sessions, users } from "../../database/schemas";
+
+@Injectable()
+export class PurgeService {
+	private readonly logger = new Logger(PurgeService.name);
+
+	constructor(private readonly databaseService: DatabaseService) {}
+
+	// Toutes les nuits à minuit
+	@Cron(CronExpression.EVERY_DAY_AT_MIDNIGHT)
+	async purgeExpiredData() {
+		this.logger.log("Starting automatic data purge...");
+
+		try {
+			const now = new Date();
+
+			// 1. Purge des sessions expirées
+			const deletedSessions = await this.databaseService.db
+				.delete(sessions)
+				.where(lte(sessions.expiresAt, now))
+				.returning();
+			this.logger.log(`Purged ${deletedSessions.length} expired sessions.`);
+
+			// 2. Purge des signalements obsolètes
+			const deletedReports = await this.databaseService.db
+				.delete(reports)
+				.where(lte(reports.expiresAt, now))
+				.returning();
+			this.logger.log(`Purged ${deletedReports.length} obsolete reports.`);
+
+			// 3. Purge des utilisateurs supprimés (Soft Delete > 30 jours)
+			const thirtyDaysAgo = new Date();
+			thirtyDaysAgo.setDate(thirtyDaysAgo.getDate() - 30);
+
+			const deletedUsers = await this.databaseService.db
+				.delete(users)
+				.where(
+					and(eq(users.status, "deleted"), lte(users.deletedAt, thirtyDaysAgo)),
+				)
+				.returning();
+			this.logger.log(
+				`Purged ${deletedUsers.length} users marked for deletion more than 30 days ago.`,
+			);
+
+			// 4. Purge des contenus supprimés (Soft Delete > 30 jours)
+			const deletedContents = await this.databaseService.db
+				.delete(contents)
+				.where(
+					and(isNotNull(contents.deletedAt), lte(contents.deletedAt, thirtyDaysAgo)),
+				)
+				.returning();
+			this.logger.log(
+				`Purged ${deletedContents.length} contents marked for deletion more than 30 days ago.`,
+			);
+		} catch (error) {
+			this.logger.error("Error during data purge", error);
+		}
+	}
+}