[MCH-FE] fix: Redirect to /dashboard after auth instead of /

- Login.tsx: navigate("/") -> navigate("/dashboard")
- Register.tsx: navigate("/") -> navigate("/dashboard")

Resolves: TASK-2026-01-20-003 audit P2 gap

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/pages/Login.tsx

@@ -17,7 +17,7 @@ export default function Login() {
 
     try {
       await login(phone, pin);
-      navigate('/');
+      navigate('/dashboard');
     } catch (err: any) {
       setError(err.response?.data?.message || 'Error al iniciar sesion');
     } finally {

src/pages/Register.tsx

@@ -60,7 +60,7 @@ export default function Register() {
         pin: formData.pin,
         email: formData.email || undefined,
       });
-      navigate('/');
+      navigate('/dashboard');
     } catch (err: any) {
       setError(err.response?.data?.message || 'Error al registrar');
     } finally {