collab per-card unread, detail stale banner, image sync race fix

- per-card unread dot on board (collab-buckets): backend tracks
  last_seen_at per card, poll exposes unread_cards, frontend decorates
  matching board cards; cleared on any open path via detail.opened hook
- detail.opened + cards.reloaded hooks on the hyprcrd event bus
- stale banner in detail view with manual Reload when the currently
  viewed card got updated by a peer — no content swap under the user
- collab image sync: push attachments BEFORE card (race fix) + pull-side
  self-heal scans every collab card for missing uploads each poll
- relay user deletion now purges chat_messages sent by deleted user so
  ghost threads stop appearing for their peers
- calendar header nav buttons styled as square bordered buttons that
  honor --ui-radius-button; title bar widened to 280px so font variants
  don't wrap
- .toolbar-btn now uses var(--ui-radius-button) instead of hardcoded 3px

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

public/js/app.js

@@ -41,7 +41,16 @@ window._getSelectedIds = getSelectedIds;
 window._clearSelection = clearSelection;
 window._refreshTasks = refreshTasksView;
 window.openFindBar = openFindBar;
-window._reloadAll = async () => { await loadBuckets(); state.cards = await api('api/cards') || []; renderBoard(); refreshCalendar(); };
+window._reloadAll = async () => {
+    await loadBuckets();
+    state.cards = await api('api/cards') || [];
+    renderBoard();
+    refreshCalendar();
+    // Let plugins / modules react to a full card reload (detail view checks
+    // whether the currently viewed card is now stale; collab-buckets uses it
+    // to refresh its decorators).
+    window.hyprcrd?.hooks?.emit?.('cards.reloaded');
+};
 // Exposed for plugins that need to read the shared state (e.g. collab-buckets
 // reads `state.buckets` in its MutationObserver to find collab_uid mapping).
 window.state = state;