Add Web Push notifications, PWA support, and full-screen tablet kiosk

Parents get a real push notification when a kid checks off a task
(false->true transitions only, fire-and-forget, degrades gracefully with
no VAPID keys configured). Dashboard is a fully installable iOS/Android
PWA; each child's kiosk link gets its own dynamic per-token manifest so
"Add to Home Screen" opens straight into their board in standalone mode.

Kiosk view is reworked for tablets: safe-area-aware full-bleed layout,
the whole task row is now tappable (previously only the 24px checkbox
was, well under Apple's touch-target minimum), and app icons are
generated by a small dependency-free PNG encoder (no image tooling
available in this environment).

Push requires real HTTPS (iOS Safari won't allow it otherwise) - README
and UNRAID.md cover VAPID setup and the HTTPS prerequisite.

public/js/calendarRender.js

@@ -49,6 +49,17 @@ function renderCalendar({ calendar, editable, weekdayBoard, weekendWrap, handler
     row.appendChild(cb);
     row.appendChild(span);
 
+    if (!editable) {
+      // Kiosk mode: the 24px checkbox alone is a poor touch target, so the
+      // whole row toggles it. Skip when the tap landed on the checkbox
+      // itself — it already handles its own toggle+change natively.
+      row.addEventListener('click', (e) => {
+        if (e.target === cb) return;
+        cb.checked = !cb.checked;
+        cb.dispatchEvent(new Event('change'));
+      });
+    }
+
     if (editable) {
       span.contentEditable = 'true';
       span.addEventListener('keydown', (e) => {