Delete exercise 21-24 and add 5 new beginner JavaScript exercises (21-25)

- Exercise 21: Your First Array - Introduction to arrays and indexing
- Exercise 22: Array Methods - push, pop, shift, unshift, and length
- Exercise 23: Your First Object - Object literals and properties
- Exercise 24: For...of Loop - Iterating through arrays and strings
- Exercise 25: String Methods - Common string manipulation methods

Each exercise includes README (EN/ES), app.js, solution.hide.js, and tests.js

Author: ehiber

exercises/21-Russian_Roulette/README.es.md

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+---
+tutorial: "https://www.youtube.com/watch?v=prIqHDmw5r0"
+---
+
+# `21` Tu Primer Array
+
+Un array es una lista de valores. Los arrays son una de las estructuras de datos más importantes en programación porque nos permiten almacenar múltiples valores en una sola variable.
+
+Los arrays se declaran con corchetes `[]` y pueden contener cualquier tipo de dato:
+
+```js
+let fruits = ["manzana", "plátano", "naranja"];
+let numeros = [1, 2, 3, 4, 5];
+let mixto = [1, "hola", true, 3.14];
+```
+
+Puedes acceder a cada elemento en un array usando su **índice** (posición). Recuerda que los índices comienzan en `0`:
+
+```js
+let fruits = ["manzana", "plátano", "naranja"];
+console.log(fruits[0]); // "manzana"
+console.log(fruits[1]); // "plátano"
+console.log(fruits[2]); // "naranja"
+```
+
+## 📝 Instrucciones:
+
+1. Crea un array llamado `colors` con al menos 3 nombres de colores como strings.
+2. Usa `console.log()` para imprimir cada color accediendo por su posición de índice.
+3. Imprime el array completo en la consola.
+
+## Ejemplo:
+
+```js
+let animals = ["perro", "gato", "pájaro"];
+console.log(animals[0]); // "perro"
+console.log(animals[1]); // "gato"
+console.log(animals[2]); // "pájaro"
+console.log(animals);    // ["perro", "gato", "pájaro"]
+```
+
+## 💡 Pista:
+
++ Recuerda: los índices de arrays comienzan en 0, ¡no en 1!
++ Puedes almacenar cualquier tipo de dato dentro de un array.
+

exercises/21-Russian_Roulette/README.md

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+---
+tutorial: "https://www.youtube.com/watch?v=prIqHDmw5r0"
+---
+
+# `21` Your First Array
+
+An array is a list of values. Arrays are one of the most important data structures in programming because they allow us to store multiple values in a single variable.
+
+Arrays are declared with square brackets `[]` and can hold any type of data:
+
+```js
+let fruits = ["apple", "banana", "orange"];
+let numbers = [1, 2, 3, 4, 5];
+let mixed = [1, "hello", true, 3.14];
+```
+
+You can access each element in an array using its **index** (position). Remember that indices start at `0`:
+
+```js
+let fruits = ["apple", "banana", "orange"];
+console.log(fruits[0]); // "apple"
+console.log(fruits[1]); // "banana"
+console.log(fruits[2]); // "orange"
+```
+
+## 📝 Instructions:
+
+1. Create an array called `colors` with at least 3 color names as strings.
+2. Use `console.log()` to print each color accessing it by its index position.
+3. Print the array itself to the console.
+
+## Example:
+
+```js
+let animals = ["dog", "cat", "bird"];
+console.log(animals[0]); // "dog"
+console.log(animals[1]); // "cat"
+console.log(animals[2]); // "bird"
+console.log(animals);    // ["dog", "cat", "bird"]
+```
+
+## 💡 Hint:
+
++ Remember: array indexes start at 0, not 1!
++ You can store any type of data inside an array.
+

exercises/21-Russian_Roulette/app.js

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+//Create an array with at least 3 colors
+let colors = [];
+
+//access and print each color by its index
+
+//print the array
+//your code here
+

exercises/21-Russian_Roulette/solution.hide.js

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+//Create an array with at least 3 colors
+let colors = ["red", "blue", "green"];
+
+//access and print each color by its index
+console.log(colors[0]);
+console.log(colors[1]);
+console.log(colors[2]);
+
+//print the array
+console.log(colors);

exercises/21-Russian_Roulette/tests.js

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+
+const fs = require('fs');
+const path = require('path');
+
+jest.dontMock('fs');
+let _buffer = "";
+let _log = console.log;
+
+global.console.log = console.log = jest.fn((text) => _buffer += text + "\n");
+
+describe('Array exercise', function () {
+    afterEach(() => { jest.resetModules(); });
+
+    it('Should have an array called "colors"', function () {
+        const appPath = path.join(__dirname, './app.js');
+        const appContent = fs.readFileSync(appPath, 'utf8');
+        expect(appContent).toMatch(/let\s+colors\s*=\s*\[/);
+    });
+
+    it('Should print at least 3 elements from the colors array', function () {
+        _buffer = "";
+        const { colors } = require('./app.js');
+        const logs = _buffer.trim().split('\n');
+        expect(logs.length).toBeGreaterThanOrEqual(3);
+    });
+
+    it('Should print the array itself', function () {
+        _buffer = "";
+        require('./app.js');
+        expect(_buffer).toMatch(/,/); // arrays have commas when printed
+    });
+});