fix(ux): microinteraction fixes - swipe hint, locale loading, haptics, weather toast, FAB backdrop

- tasks.js: add maybeShowSwipeHint (long loop, max 3x) - matches shopping.js pattern
- tasks.js: vibrate(15) on task status toggle
- oikos-locale-picker: show disabled/loading state for both reload and setLocale paths
- dashboard: show success toast after weather refresh (all 4 locales)
- dashboard: add semi-transparent FAB backdrop to signal open mode

public/components/oikos-locale-picker.js

@@ -54,9 +54,9 @@ class OikosLocalePicker extends HTMLElement {
     }
 
     select.addEventListener('change', () => {
+      select.disabled = true;
+      select.style.opacity = '0.5';
       if (select.value === 'system') {
-        select.disabled = true;
-        select.style.opacity = '0.5';
         localStorage.removeItem('oikos-locale');
         // Kurze Verzögerung damit der Browser den disabled-Zustand rendert
         setTimeout(() => location.reload(), 60);