sync-event toasts, image pull ordering, stale banner field diff

- replace chat-bot sync notifications with a dedicated relay_sync_events
  queue: POST/GET /api/sync-events, drained by /api/relay/poll and
  surfaced as stacking toasts via caldav.js. Old /api/chat/bot removed,
  bot=1 rows purged on bootstrap, orange bot rendering dropped from
  relay UI. Chat thread stays clean.
- collab pull: fetch attachments BEFORE applying the body so the moment
  state.cards reflects the new reference the file is on disk. Fixes the
  "preview shows broken/missing image, editor shows it" race where the
  browser cached the 404 between attachment landing and user re-render.
- detail stale banner now compares title/body/color/tags in addition to
  updated_at — robust against second-granularity timestamp collisions
  and any other case where updated_at doesn't tick but content differs.

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

relay/ui/app.js

@@ -719,20 +719,12 @@ async function loadChatHistory(peer, quiet = false) {
         return;
     }
 
-    container.innerHTML = messages.map(m => {
-        if (m.bot) {
-            return `
-        <div class="chat-msg bot">
-            <div><i class="ph ph-robot"></i> ${escapeHtml(m.body)}</div>
-            <div class="msg-time">${formatChatTime(m.created_at)}</div>
-        </div>`;
-        }
-        return `
+    container.innerHTML = messages.map(m => `
         <div class="chat-msg ${m.mine ? 'mine' : 'theirs'}">
             <div>${escapeHtml(m.body)}</div>
             <div class="msg-time">${formatChatTime(m.created_at)}${m.mine && m.seen ? ' <i class="ph ph-checks"></i>' : ''}</div>
-        </div>`;
-    }).join('');
+        </div>
+    `).join('');
 
     if (wasAtBottom || !quiet) {
         container.scrollTop = container.scrollHeight;