Add jefe mecánico to client booking flow

Cliente now picks a jefe mecánico after choosing the service so the
calendar shows that specific jefe's availability. Each jefe has its own
configurable parallel slot capacity (replacing the global SLOTS_PARALELOS
= 5). Admins manage jefes from /admin/jefes; jefes log in to /jefe to
see their daily agenda.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/lib/auth-admin.ts

@@ -19,6 +19,14 @@ export async function crearSesionCliente(clienteId: string): Promise<string> {
   return token;
 }
 
+export async function crearSesionJefe(jefeId: string): Promise<string> {
+  const token = await new SignJWT({ sub: jefeId, role: "jefe" })
+    .setProtectedHeader({ alg: "HS256" })
+    .setExpirationTime("8h")
+    .sign(SECRET);
+  return token;
+}
+
 export async function verificarSesion(
   cookieName: string
 ): Promise<{ sub: string; role: string } | null> {