feat: add archive reader and tests

- Añade `archiveReader` que lista entradas en ZIP/7z con fallback a `unzip`
- Añade tests unitarios que mockean `child_process.exec` para validar parsing
- Documenta dependencia de binarios en README y CI (pasos previos)

backend/tests/services/archiveReader.spec.ts

@@ -0,0 +1,47 @@
+import { describe, it, expect, vi } from 'vitest';
+
+// Mockeamos el módulo `child_process` para controlar las llamadas a `exec`.
+vi.mock('child_process', () => ({ exec: vi.fn() }));
+import * as child_process from 'child_process';
+import { listArchiveEntries } from '../../src/services/archiveReader';
+
+describe('services/archiveReader', () => {
+  it('lista entradas usando 7z -slt', async () => {
+    const stdout = `Path = file1.txt\nSize = 123\nPacked Size = 0\n\nPath = dir/file2.bin\nSize = 456\nPacked Size = 0\n`;
+
+    (child_process as any).exec.mockImplementation((cmd: any, cb: any) => {
+      cb(null, stdout, '');
+      return {} as any;
+    });
+
+    const entries = await listArchiveEntries('/roms/archive.7z', console);
+    expect(entries.length).toBe(2);
+    expect(entries[0].name).toBe('file1.txt');
+    expect(entries[0].size).toBe(123);
+    (child_process as any).exec.mockRestore?.();
+  });
+
+  it('usa unzip como fallback para zip cuando 7z falla', async () => {
+    (child_process as any).exec
+      .mockImplementationOnce((cmd: any, cb: any) => {
+        // simular fallo de 7z
+        cb(new Error('7z not found'), '', '');
+        return {} as any;
+      })
+      .mockImplementationOnce((cmd: any, cb: any) => {
+        // salida simulada de unzip -l
+        cb(null, '   123 file1.txt\n   456 file2.bin\n', '');
+        return {} as any;
+      });
+
+    const entries = await listArchiveEntries('/roms/archive.zip', console);
+    expect(entries.length).toBe(2);
+    expect(entries[0].name).toBe('file1.txt');
+    (child_process as any).exec.mockRestore?.();
+  });
+
+  it('retorna vacío para formatos no soportados', async () => {
+    const entries = await listArchiveEntries('/roms/simple.bin');
+    expect(entries).toEqual([]);
+  });
+});