fix(fitness): persist activityType when picking GPS activity

The active-workout activity picker updated local state + workout.name
but never synced workout.activityType, so every hiking/walking/cycling
workout was saved with an inner exercise of 'running'. That silently
applied the wrong kcal model — running Minetti for hiking/walking
(~43% overestimate) and running instead of the cycling physics model
(large overestimate for cycling).

Adds an activityType setter on the workout store and invokes it from
selectActivity() so the saved session's exercise matches the picked
activity.

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "homepage",
-	"version": "1.37.5",
+	"version": "1.37.6",
 	"private": true,
 	"type": "module",
 	"scripts": {

src/lib/js/workout.svelte.ts

@@ -714,6 +714,7 @@ export function createWorkout() {
 		get paused() { return paused; },
 		get mode() { return mode; },
 		get activityType() { return activityType; },
+		set activityType(v: GpsActivityType | null) { activityType = v; _persist(); },
 		get name() { return name; },
 		set name(v: string) { name = v; _persist(); },
 		get templateId() { return templateId; },

src/routes/fitness/[workout=fitnessWorkout]/[active=fitnessActive]/+page.svelte

@@ -252,6 +252,7 @@
 	function selectActivity(/** @type {string} */ id) {
 		selectedActivity = /** @type {import('$lib/js/workout.svelte').GpsActivityType} */ (id);
 		const labels = { running: 'Running', walking: 'Walking', cycling: 'Cycling', hiking: 'Hiking' };
+		workout.activityType = selectedActivity;
 		workout.name = labels[selectedActivity] ?? 'GPS Workout';
 		showActivityPicker = false;
 	}