Show expected vs actual pace/HR per lap in the Review Queue

Activities recorded from a structured Garmin workout carry a workoutId;
when its steps line up 1:1 with the recorded laps, the per-step target
pace/HR zone is resolved (via a Karvonen lookup for named zones) and stored
on each lap. The Review Queue plots it against the actual per-lap pace/HR
so the user can eyeball whether a run matches its plan while sorting it.

backend/internal/garmin/client.go

@@ -36,6 +36,8 @@ type Client interface {
 	GetActivitySplits(ctx context.Context, activityID int64) (ActivitySplits, error)
 	// GetActivityDetails fetches raw per-second telemetry for one activity.
 	GetActivityDetails(ctx context.Context, activityID int64) (ActivityDetails, error)
+	// GetWorkoutByID fetches a structured workout's step-by-step plan.
+	GetWorkoutByID(ctx context.Context, workoutID int64) (Workout, error)
 	// Close terminates the subprocess, if running.
 	Close() error
 }
@@ -270,6 +272,27 @@ func (c *mcpClient) GetActivityDetails(ctx context.Context, activityID int64) (A
 	return details, nil
 }
 
+func (c *mcpClient) GetWorkoutByID(ctx context.Context, workoutID int64) (Workout, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if err := c.ensureStarted(ctx); err != nil {
+		return Workout{}, err
+	}
+	msg, err := c.callTool(ctx, "get_workout_by_id", map[string]any{
+		"workout_id": strconv.FormatInt(workoutID, 10),
+	})
+	if err != nil {
+		return Workout{}, err
+	}
+
+	var workout Workout
+	if err := json.Unmarshal([]byte(msg), &workout); err != nil {
+		return Workout{}, fmt.Errorf("get_workout_by_id did not return valid JSON (%q): %w", truncate(msg, 200), err)
+	}
+	return workout, nil
+}
+
 func (c *mcpClient) Close() error {
 	c.mu.Lock()
 	defer c.mu.Unlock()