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/locales/en.json

@@ -65,6 +65,7 @@
     "loadError": "Dashboard could not be fully loaded.",
     "weatherRefresh": "Refresh weather",
     "weatherRefreshTitle": "Refresh",
+    "weatherUpdated": "Weather updated",
     "weatherFeelsLike": "Feels like {{temp}}° · {{humidity}}% · Wind {{wind}} km/h",
     "fabTaskLabel": "Add task",
     "fabCalendarLabel": "Add event",