Fix login blank screen and progress persistence

- Fix authStore to persist user data, not just isAuthenticated
- Fix progressStore handling of undefined API responses
- Remove minimax.md documentation file
- All progress now properly saves to PostgreSQL
- Login flow working correctly

backend/internal/handlers/users.go

@@ -216,7 +216,7 @@ func (h *UsersHandler) GetUserProgreso(c *gin.Context) {
 		return
 	}
 
-	progresos, err := h.progresoRepo.GetByUsuarioID(c.Request.Context(), id)
+	progresos, err := h.progresoRepo.GetProgresoByUsuarioID(id)
 	if err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "Error al obtener progreso"})
 		return