feat(auth): add optional authentication guard and extend AuthModule providers

Introduce `OptionalAuthGuard` to allow conditional authentication for routes. Update `AuthModule` to include `AuthGuard`, `OptionalAuthGuard`, and `RolesGuard` in providers and exports for broader reuse.

feat(app): integrate `AdminModule` into app module

Add `AdminModule` to the app's main module to enable administration functionalities.

feat(users): enhance user profiles with bio and avatar fields

Extend `UpdateUserDto` to include optional `bio` and `avatarUrl` fields for better user customization.

feat(categories): add functionality to count all categories

Implement `countAll` method in `CategoriesRepository` to fetch the total number of categories using raw SQL counting.

backend/src/auth/guards/optional-auth.guard.ts

@@ -0,0 +1,43 @@
+import {
+	CanActivate,
+	ExecutionContext,
+	Injectable,
+} from "@nestjs/common";
+import { ConfigService } from "@nestjs/config";
+import { getIronSession } from "iron-session";
+import { JwtService } from "../../crypto/services/jwt.service";
+import { getSessionOptions, SessionData } from "../session.config";
+
+@Injectable()
+export class OptionalAuthGuard implements CanActivate {
+	constructor(
+		private readonly jwtService: JwtService,
+		private readonly configService: ConfigService,
+	) {}
+
+	async canActivate(context: ExecutionContext): Promise<boolean> {
+		const request = context.switchToHttp().getRequest();
+		const response = context.switchToHttp().getResponse();
+
+		const session = await getIronSession<SessionData>(
+			request,
+			response,
+			getSessionOptions(this.configService.get("SESSION_PASSWORD") as string),
+		);
+
+		const token = session.accessToken;
+
+		if (!token) {
+			return true;
+		}
+
+		try {
+			const payload = await this.jwtService.verifyJwt(token);
+			request.user = payload;
+		} catch {
+			// Ignore invalid tokens for optional auth
+		}
+
+		return true;
+	}
+}