feat: add streamArchiveEntry to archiveReader and tests

- Añade `streamArchiveEntry` que devuelve un stream para entradas internas de ZIP/7z
- Añade tests unitarios que mockean `child_process.spawn` (7z + unzip fallback)
- Mantiene `listArchiveEntries` y documenta dependencia de binarios en CI

backend/tests/services/archiveReader.stream.spec.ts

@@ -0,0 +1,69 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { PassThrough } from 'stream';
+import { EventEmitter } from 'events';
+
+vi.mock('child_process', () => ({ spawn: vi.fn() }));
+import * as child_process from 'child_process';
+import { streamArchiveEntry } from '../../src/services/archiveReader';
+
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
+describe('services/archiveReader streamArchiveEntry', () => {
+  it('streams entry using 7z stdout', async () => {
+    const pass = new PassThrough();
+    const proc = new EventEmitter() as any;
+    proc.stdout = pass;
+
+    (child_process.spawn as any).mockImplementation(() => proc as any);
+
+    // Emular producción de datos de forma asíncrona
+    setImmediate(() => {
+      pass.write(Buffer.from('content-from-7z'));
+      pass.end();
+    });
+
+    const stream = await streamArchiveEntry('/roms/archive.7z', 'path/file.txt');
+    expect(stream).not.toBeNull();
+
+    const chunks: Buffer[] = [];
+    for await (const chunk of stream as any) {
+      chunks.push(Buffer.from(chunk));
+    }
+
+    expect(Buffer.concat(chunks).toString()).toBe('content-from-7z');
+  });
+
+  it('falls back to unzip -p when 7z throws', async () => {
+    const pass = new PassThrough();
+    const proc2 = new EventEmitter() as any;
+    proc2.stdout = pass;
+
+    (child_process.spawn as any)
+      .mockImplementationOnce(() => {
+        throw new Error('spawn ENOENT');
+      })
+      .mockImplementationOnce(() => proc2 as any);
+
+    setImmediate(() => {
+      pass.write(Buffer.from('fallback-content'));
+      pass.end();
+    });
+
+    const stream = await streamArchiveEntry('/roms/archive.zip', 'file.dat');
+    expect(stream).not.toBeNull();
+
+    const chunks: Buffer[] = [];
+    for await (const chunk of stream as any) {
+      chunks.push(Buffer.from(chunk));
+    }
+
+    expect(Buffer.concat(chunks).toString()).toBe('fallback-content');
+  });
+
+  it('returns null for unsupported formats', async () => {
+    const res = await streamArchiveEntry('/roms/archive.bin', 'entry');
+    expect(res).toBeNull();
+  });
+});