feat: import job runner in-memory

- Añade ImportRunner en memoria con concurrencia configurable
- Tests TDD para enqueue, concurrencia y comportamiento tras stop
- Actualiza /api/import/scan para encolar jobs y registrar errores
- Ajusta tsconfig.json para incluir tests en comprobaciones de tipo

backend/tests/routes/import.spec.ts

@@ -0,0 +1,19 @@
+import { describe, it, expect } from 'vitest';
+import { buildApp } from '../../src/app';
+
+describe('routes/import', () => {
+  it('POST /api/import/scan devuelve 202 o 200', async () => {
+    const app = buildApp();
+    await app.ready();
+
+    const res = await app.inject({
+      method: 'POST',
+      url: '/api/import/scan',
+      payload: { persist: false },
+    });
+
+    expect([200, 202]).toContain(res.statusCode);
+
+    await app.close();
+  });
+});