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/categories/repositories/categories.repository.ts

@@ -1,5 +1,5 @@
 import { Injectable } from "@nestjs/common";
-import { eq } from "drizzle-orm";
+import { eq, sql } from "drizzle-orm";
 import { DatabaseService } from "../../database/database.service";
 import { categories } from "../../database/schemas";
 import type { CreateCategoryDto } from "../dto/create-category.dto";
@@ -16,6 +16,13 @@ export class CategoriesRepository {
 			.orderBy(categories.name);
 	}
 
+	async countAll() {
+		const result = await this.databaseService.db
+			.select({ count: sql<number>`count(*)` })
+			.from(categories);
+		return Number(result[0].count);
+	}
+
 	async findOne(id: string) {
 		const result = await this.databaseService.db
 			.select()