fix: audit 89 bugs - critical fixes

CRITICAL:
- JwtMiddleware orden (antes de UseAuthentication)
- JWT Secret en appsettings.json (no vacio)
- Transbank MySQL connection string (User=root + placeholder)
- package-lock generado + Dockerfile usa npm install
- Tests E2E: selectores corregidos con name attributes
- Tests: rut invalido reemplazado, casos sin auth
- Contacto page: apunta a services-externos (no backend)
- .env.example: credenciales reales -> placeholders

HIGH:
- extra_hosts agregado a services-externos en compose
- Dockerfile frontend: npm ci -> npm install

frontend/Dockerfile

@@ -1,7 +1,7 @@
 FROM node:20-alpine AS build
 WORKDIR /app
 COPY package*.json ./
-RUN npm ci
+RUN npm install
 COPY . .
 RUN npm run build
 

frontend/src/app/contacto/page.tsx

@@ -1,21 +1,30 @@
 'use client';
 
 import { useState, FormEvent } from 'react';
-import { api } from '@/services/api';
+
+const SERVICES_URL = process.env.NEXT_PUBLIC_SERVICES_URL || 'http://localhost:5001/api';
 
 export default function ContactoPage() {
   const [mail, setMail] = useState('');
   const [mensaje, setMensaje] = useState('');
+  const [enviando, setEnviando] = useState(false);
 
   const handleSubmit = async (e: FormEvent) => {
     e.preventDefault();
+    setEnviando(true);
     try {
-      await api.post('/email/send', { to: mail, subject: 'Contacto desde SAM', body: mensaje });
+      await fetch(`${SERVICES_URL}/email/send`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ to: mail, subject: 'Contacto desde SAM', body: mensaje }),
+      });
       alert('Correo enviado');
       setMail('');
       setMensaje('');
     } catch {
       alert('Error al enviar');
+    } finally {
+      setEnviando(false);
     }
   };
 

frontend/src/app/login/page.tsx

@@ -50,11 +50,11 @@ export default function LoginPage() {
               <form onSubmit={handleSubmit}>
                 <div className="mb-3">
                   <label className="form-label">RUT</label>
-                  <input className="form-control" value={rut} onChange={handleRutChange} placeholder="12.345.678-5" />
+                  <input name="rut" className="form-control" value={rut} onChange={handleRutChange} placeholder="12.345.678-5" />
                 </div>
                 <div className="mb-3">
                   <label className="form-label">Clave</label>
-                  <input type="password" className="form-control" value={clave} onChange={e => setClave(e.target.value)} />
+                  <input type="password" name="clave" className="form-control" value={clave} onChange={e => setClave(e.target.value)} />
                 </div>
                 {error && <div className="alert alert-danger py-2">{error}</div>}
                 <button type="submit" className="btn btn-primary w-100">Ingresar</button>