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/users/dto/update-user.dto.ts

@@ -5,4 +5,13 @@ export class UpdateUserDto {
 	@IsString()
 	@MaxLength(32)
 	displayName?: string;
+
+	@IsOptional()
+	@IsString()
+	@MaxLength(255)
+	bio?: string;
+
+	@IsOptional()
+	@IsString()
+	avatarUrl?: string;
 }