fix(activities): favorites tab shows login toast instead of navigating when logged out

Tapping Favorites used to drop the user onto an empty page that
*then* fired the auth-prompt toast on mount — the navigation was
wasted motion. Mirror the Create tab pattern: onClick checks auth
first, fires the same toast (with Log in action) when unauthed,
and only router-pushes when authed.

`path` is kept on the tab so the active-highlight still works when
the user is actually on /activities/favorites after logging in
(BottomNav highlights via tab.path && isActive(tab.path)). The
mount-time toast on ActivitiesFavoritesPage stays as a defensive
fallback for direct URL access.

src/activities-app/App.vue

@@ -54,7 +54,27 @@ const tabs = computed<BottomTab[]>(() => [
     disabled: !isAuthenticated.value,
   },
   { name: t('activities.nav.map'), icon: Map, path: '/activities/map' },
-  { name: t('activities.nav.favorites'), icon: Heart, path: '/activities/favorites' },
+  {
+    name: t('activities.nav.favorites'),
+    icon: Heart,
+    // path kept so the tab stays active-highlighted while the user is
+    // on /activities/favorites; onClick wins for the actual tap so we
+    // can gate on auth (mirrors the Create tab pattern above).
+    path: '/activities/favorites',
+    onClick: () => {
+      if (!isAuthenticated.value) {
+        toast.info(t('activities.favorites.loginPrompt'), {
+          action: {
+            label: t('activities.favorites.logIn'),
+            onClick: () => router.push('/login'),
+          },
+        })
+        return
+      }
+      router.push('/activities/favorites')
+    },
+    disabled: !isAuthenticated.value,
+  },
 ])
 
 // Feed tab is active for the bare /activities route AND all sub-paths that