fixes: tag assign stale body, board placeholder, plugin pending, bucket activate

- Context menu tag toggle reads fresh body from state.cards — was
  overwriting with stale snapshot, dropping existing tags (e.g. #done)
- Board empty-state centered with flex (vertical + horizontal)
- Plugin settings: batch toggles via Apply button, single reload
  instead of one reload per toggle
- New bucket creation activates it directly on the board

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/js/modules/buckets.js

@@ -608,8 +608,13 @@ function renderBar() {
         }
         const name = await showDialog({ title: 'new_bucket', input: true, placeholder: '> bucket name...' });
         if (!name || !name.trim()) return;
-        await api('api/buckets', { method: 'POST', body: { name: name.trim() } });
+        const created = await api('api/buckets', { method: 'POST', body: { name: name.trim() } });
         await loadBuckets();
+        if (created?.id) {
+            setActiveBucket(created.id);
+            state.activeGroup = null;
+        }
+        renderBar();
         window._renderBoard();
     });