fix: anchor overdue badge to icon via runtime wrapper (#56)

Root cause: the badge was `position: absolute` relative to the entire
`.nav-item`, which stretches to `flex: 1` on mobile (up to ~75 px wide).
With `right: 4px` the badge sat far from the icon on the bottom bar and
overlapped label text in the expanded desktop sidebar.

Fix: `updateOverdueBadge()` now wraps the nav icon in a
`.nav-item__icon-wrap` span (created once, reused on subsequent calls).
The badge is appended there instead of to the nav item root.

CSS changes:
- Remove `.nav-item .nav-badge` positional override
- Add `.nav-item__icon-wrap { position: relative; display: inline-flex }`
- Add `.nav-item__icon-wrap .nav-badge { position: absolute; top: -4px; right: -4px }`

The badge now consistently overlays the top-right corner of the icon
across all nav layouts (mobile column, collapsed sidebar row, expanded
sidebar row with label).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/pages/tasks.js

@@ -827,11 +827,23 @@ function updateOverdueBadge() {
 
   document.querySelectorAll('[data-route="/tasks"] .nav-badge').forEach((el) => el.remove());
   if (overdue > 0) {
-    document.querySelectorAll('[data-route="/tasks"]').forEach((el) => {
+    document.querySelectorAll('[data-route="/tasks"]').forEach((navItem) => {
+      let anchor = navItem.querySelector('.nav-item__icon-wrap');
+      if (!anchor) {
+        const icon = navItem.querySelector('.nav-item__icon');
+        anchor = document.createElement('span');
+        anchor.className = 'nav-item__icon-wrap';
+        if (icon) {
+          icon.replaceWith(anchor);
+          anchor.appendChild(icon);
+        } else {
+          navItem.prepend(anchor);
+        }
+      }
       const badge = document.createElement('span');
       badge.className = 'nav-badge';
       badge.textContent = String(overdue);
-      el.appendChild(badge);
+      anchor.appendChild(badge);
     });
   }
 }