feat: allow editing frequency and target_value on habits

- Add frequency to UpdateHabitRequest (was immutable, now editable)
- Validate frequency + specific_days/dates coherence on update
- Keep type and is_negative immutable (they change entry semantics)
- Remove completion_rate references from swagger and README

internal/infrastructure/http/habit_handlers.go

@@ -313,10 +313,11 @@ func (h *HabitHandlers) UpdateHabit(w http.ResponseWriter, r *http.Request) {
 		UserID:        userID,
 		Name:          req.Name,
 		Description:   req.Description,
-		CarryOver:     req.CarryOver,
-		TargetValue:   req.TargetValue,
+		Frequency:     req.Frequency,
 		SpecificDays:  req.SpecificDays,
 		SpecificDates: req.SpecificDates,
+		CarryOver:     req.CarryOver,
+		TargetValue:   req.TargetValue,
 	}
 
 	if err := h.updateHandler.Handle(r.Context(), cmd); err != nil {